This adds a third passenger to the willy who has a browning.

Things in Blue I have added to the willy/objects.con file.
I basically copied the browning from the sherman and put it into the Willy. It is obviously not in the right position, but with a little tweaking it can be moved.
rem *** Willy ***
ObjectTemplate.create PlayerControlObject Willy
ObjectTemplate.NameTagOffset -0.3/-0.2/0
ObjectTemplate.setNetworkableInfo WillyBodyInfo
ObjectTemplate.saveInSeparateFile 1
objectTemplate.cullRadiusScale 5
ObjectTemplate.hasMobilePhysics 1
ObjectTemplate.hasDynamicShadow 1
ObjectTemplate.explosionRadius 8
ObjectTemplate.explosionDamage 5
ObjectTemplate.damageFromWater 1
ObjectTemplate.drag 1.5
ObjectTemplate.mass 2500
ObjectTemplate.hasCollisionPhysics 1
ObjectTemplate.hasResponsePhysics 1
ObjectTemplate.hasArmor 1
ObjectTemplate.speedMod 1
ObjectTemplate.exitTimer 0.75
ObjectTemplate.hitpoints 50
ObjectTemplate.maxhitpoints 50
ObjectTemplate.material 45
ObjectTemplate.criticalDamage 6
ObjectTemplate.hpLostWhileCriticalDamage 2
ObjectTemplate.explosionForceMod 20
ObjectTemplate.hpLostWhileUpSideDown 5
ObjectTemplate.hpLostWhileDamageFromWater 5
ObjectTemplate.addArmorEffect 30 e_WillyDamage 0/1.7/0
ObjectTemplate.addArmorEffect 6 e_WillyFire 0/0.5/0.8
ObjectTemplate.addArmorEffect 0 e_scrapmetal_willy 0/0/0
ObjectTemplate.addArmorEffect 0 e_ExplGas 0/1.2/0
ObjectTemplate.addArmorEffect -1 WaterWaterExplosion 0/0/0
ObjectTemplate.aiTemplate Willy
rem -------------------------------------
ObjectTemplate.addTemplate lodWilly
rem -------------------------------------
ObjectTemplate.setSoldierExitLocation -1.5/0/-0.8 0/0/0
ObjectTemplate.GUIIndex 26
ObjectTemplate.setVehicleIcon "Vehicle/Icon_willy.tga"
ObjectTemplate.setVehicleIconPos 40/79
ObjectTemplate.setPrimaryAmmoBar ABNone
ObjectTemplate.setCrossHairType CHTNone
ObjectTemplate.setVehicleCategory VCLand
ObjectTemplate.setVehicleType VTScoutCar
ObjectTemplate.setToolTipType TTScoutCar
ObjectTemplate.setMinimapIcon "Minimap/minimap_icon_common_16x16.tga"
ObjectTemplate.hasRestrictedExit 1

rem *** lodWilly ***
ObjectTemplate.create LodObject lodWilly
ObjectTemplate.hasMobilePhysics 1
ObjectTemplate.hasCollisionPhysics 1
ObjectTemplate.hasResponsePhysics 1
rem -------------------------------------
ObjectTemplate.addTemplate WillyComplex
ObjectTemplate.addTemplate WillySimple
ObjectTemplate.addTemplate WillyWreck
rem -------------------------------------
ObjectTemplate.lodSelector WillyLodSelector
rem *** WillyComplex ***
ObjectTemplate.create Bundle WillyComplex
ObjectTemplate.hasMobilePhysics 1
ObjectTemplate.hasCollisionPhysics 1
ObjectTemplate.hasResponsePhysics 1
rem -------------------------------------
ObjectTemplate.addTemplate lodWillyCockpit
rem ObjectTemplate.setPosition 0/0.6/-0.999
ObjectTemplate.addTemplate WillyCamera
ObjectTemplate.setPosition -0.38/0.95/-1.25
ObjectTemplate.addTemplate WillySeat
ObjectTemplate.setPosition -0.399/0.6/-0.75
ObjectTemplate.addTemplate WillyEntry
ObjectTemplate.setPosition 0/0/1
ObjectTemplate.addTemplate WillyEntry
ObjectTemplate.setPosition 0/0/-1
ObjectTemplate.addTemplate WillyPassengerPCO
ObjectTemplate.setPosition 0/0.35/-0.25
ObjectTemplate.addTemplate WillyBrowning_PCO1
ObjectTemplate.setPosition -0.30/.45/-1.15
ObjectTemplate.addTemplate WillyEngine
ObjectTemplate.setPosition 0/0.35/-0.25
ObjectTemplate.addTemplate WillySteeringDummy
ObjectTemplate.setPosition -0.399/0.35/0.15
ObjectTemplate.setRotation 0/34/0
rem -------------------------------------
rem *** lodWillyCockpit ***
ObjectTemplate.create LodObject lodWillyCockpit
rem -------------------------------------
ObjectTemplate.addTemplate WillyCockpitExternal
rem ObjectTemplate.setPosition 0/-0.95/1.25
ObjectTemplate.addTemplate WillyCockpitInternal
ObjectTemplate.setPosition 0/0.35/-0.25
rem -------------------------------------
ObjectTemplate.lodSelector WillyCockpitSelector1
rem *** WillyCockpitExternal ***
ObjectTemplate.create SimpleObject WillyCockpitExternal
ObjectTemplate.hasDynamicShadow 1
ObjectTemplate.geometry Willy_Hull_M1
rem *** WillyCockpitInternal ***
ObjectTemplate.create Bundle WillyCockpitInternal
ObjectTemplate.geometry 1P_Willy_Hul_M1
rem *** WillyCockpitSelector ***
LodSelectorTemplate.create DistCompareSelector WillyCockpitSelector1
rem LodSelectorTemplate.create DistanceSelector WillyCockpitSelector
LodSelectorTemplate.addLodDistance 3.05
LodSelectorTemplate.addLodComparison 0.5
rem *** WillyCamera ***
ObjectTemplate.create Camera WillyCamera
ObjectTemplate.setMinRotation -110/-40/0
ObjectTemplate.setMaxRotation 110/10/0
ObjectTemplate.setPivotPosition 0/0.25/0.3
ObjectTemplate.setMaxSpeed 90/90/0
ObjectTemplate.setAcceleration 5000/5000/0
ObjectTemplate.setInputToYaw c_PIMouseLookX
ObjectTemplate.setInputToPitch c_PIMouseLookY
rem *** WillySeat ***
ObjectTemplate.create SeatObject WillySeat
ObjectTemplate.seatFlags c_SeatShowFullBodySoldier
ObjectTemplate.seatFlags c_SeatIsOutside
rem *** WillyEntry ***
ObjectTemplate.create EntryPoint WillyEntry
ObjectTemplate.setEntryRadius 2.3
rem *** WillyPassengerPCO ***
ObjectTemplate.create PlayerControlObject WillyPassengerPCO
ObjectTemplate.setNetworkableInfo WillyBodyInfo
ObjectTemplate.aiTemplate WillyPassenger
rem -------------------------------------

ObjectTemplate.addTemplate WillyEntry
ObjectTemplate.setPosition 0/-0.35/1.25
ObjectTemplate.addTemplate WillyEntry
ObjectTemplate.setPosition 0/-0.35/-0.75
ObjectTemplate.addTemplate WillyCamera
ObjectTemplate.setPosition 0.3/0.6/-0.999
ObjectTemplate.addTemplate WillyPassengerSeat
ObjectTemplate.setPosition 0.3/0.25/-0.499
rem -------------------------------------
ObjectTemplate.setSoldierExitLocation 1.5/0/-0.8 0/0/0
rem ObjectTemplate.hasRestrictedExit 1
rem ObjectTemplate.altSoldierExitPosition 5.5/0/0
ObjectTemplate.GUIIndex 53
ObjectTemplate.setVehicleIcon "Vehicle/Icon_willy.tga"
ObjectTemplate.setVehicleIconPos 21/84
ObjectTemplate.setPrimaryAmmoBar ABNone
ObjectTemplate.setCrossHairType CHTNone
ObjectTemplate.setVehicleCategory VCLand
ObjectTemplate.setVehicleType VTScoutCar
ObjectTemplate.setToolTipType TTScoutCar
ObjectTemplate.setMinimapIcon "Minimap/minimap_icon_common_16x16.tga"
ObjectTemplate.hasRestrictedExit 1
rem *** WillyPassengerSeat ***
ObjectTemplate.create SeatObject WillyPassengerSeat
ObjectTemplate.seatFlags c_SeatShowFullBodySoldier
ObjectTemplate.seatFlags c_SeatIsOutside
ObjectTemplate.seatAnimationUpperBody Ub_PassengerInWilly
ObjectTemplate.seatAnimationLowerBody Lb_PassengerInWilly
rem *** willyBrowning_PCO1 ***
ObjectTemplate.create PlayerControlObject willyBrowning_PCO1
ObjectTemplate.NameTagOffset 0/-0.4/0
ObjectTemplate.setNetworkableInfo ShermanBodyInfo
ObjectTemplate.aiTemplate ShermanTopMG
rem -------------------------------------
ObjectTemplate.addTemplate willyEntry
ObjectTemplate.setPosition -0.52/-1.69/1.075
ObjectTemplate.addTemplate willyEntry
ObjectTemplate.setPosition -0.52/-1.69/-1.325
ObjectTemplate.addTemplate willyBrowning_Holder
ObjectTemplate.setPosition -0.018/-0.008/-0.353
rem -------------------------------------
ObjectTemplate.setSoldierExitLocation -2.8/-0.5/0 0/0/0
ObjectTemplate.GUIIndex 47
ObjectTemplate.setVehicleIcon "Vehicle/Icon_willy.tga"
ObjectTemplate.setVehicleIconPos 32/61
ObjectTemplate.setNumberOfWeaponIcons 1
ObjectTemplate.setPrimaryAmmoIcon "Ammo/Icon_bullet.tga"
ObjectTemplate.setPrimaryAmmoBar ABAmmoBarHeatBar
ObjectTemplate.setCrossHairType CHTCrossHair
ObjectTemplate.setVehicleCategory VCLand
ObjectTemplate.setVehicleType VTScoutCar
ObjectTemplate.setToolTipType TTLightTank
ObjectTemplate.setMinimapIcon "Minimap/minimap_icon_tank_16x16.tga"
ObjectTemplate.hasRestrictedExit 1
rem *** willyBrowning_Holder ***
ObjectTemplate.create RotationalBundle willyBrowning_Holder
ObjectTemplate.setNetworkableInfo ShermanTurretInfo
ObjectTemplate.loadSoundScript Sounds/shermanTurret.ssc
ObjectTemplate.geometry sherman_Mgun_con_m1
rem -------------------------------------
ObjectTemplate.addTemplate willy_Browning_console
ObjectTemplate.setPosition 0/0.114/-0.388
ObjectTemplate.addTemplate willyBrowningSeat
ObjectTemplate.setRotation -179.999/0/0
rem -------------------------------------
ObjectTemplate.setMaxSpeed 90/0/0
ObjectTemplate.setAcceleration 5000/0/0
ObjectTemplate.setInputToYaw c_PIMouseLookX
ObjectTemplate.setAutomaticYawStabilization 1
rem *** willy_Browning_console ***
ObjectTemplate.create RotationalBundle willy_Browning_console
ObjectTemplate.setNetworkableInfo ShermanGunInfo
ObjectTemplate.geometry Sherman_MGun_mount_M1
rem -------------------------------------
ObjectTemplate.addTemplate browning
ObjectTemplate.setPosition 0/0/-0.349
ObjectTemplate.setRotation -179.999/0/0
ObjectTemplate.addTemplate willyCamera2
ObjectTemplate.setPosition 0/0.3/0.5
ObjectTemplate.setRotation -179.999/0/0
rem -------------------------------------
ObjectTemplate.setMinRotation 180/-10/0
ObjectTemplate.setMaxRotation 280/45/0
ObjectTemplate.setMaxSpeed 0/90/0
ObjectTemplate.setAcceleration 0/-5000/0
ObjectTemplate.setInputToPitch c_PIMouseLookY
ObjectTemplate.setAutomaticPitchStabilization 1
rem *** willyCamera2 ***
ObjectTemplate.create Camera willyCamera2
ObjectTemplate.setMaxSpeed 0/0/0
ObjectTemplate.setAcceleration 0/0/0
ObjectTemplate.setInputToYaw c_PIMouseLookX
ObjectTemplate.setInputToPitch c_PIMouseLookY
rem *** willyBrowningSeat ***
ObjectTemplate.create SeatObject willyBrowningSeat
ObjectTemplate.seatFlags c_SeatIsOutside

rem *** WillyFrontWheelR ***
ObjectTemplate.create RotationalBundle WillyFrontWheelR
ObjectTemplate.setNetworkableInfo WillySteeringInfo
ObjectTemplate.hasMobilePhysics 1
ObjectTemplate.hasCollisionPhysics 1
ObjectTemplate.hasResponsePhysics 1
rem -------------------------------------
ObjectTemplate.addTemplate WillyFrontSpringR
ObjectTemplate.setPosition 0/-0.599/0
rem -------------------------------------
ObjectTemplate.setMinRotation -30/0/0
ObjectTemplate.setMaxRotation 30/0/0
ObjectTemplate.setMaxSpeed 200/0/0
ObjectTemplate.setAcceleration 200/0/0
ObjectTemplate.setInputToYaw c_PIYaw
ObjectTemplate.setAutomaticReset 1
rem *** WillyFrontWheelL ***
ObjectTemplate.create RotationalBundle WillyFrontWheelL
ObjectTemplate.setNetworkableInfo WillySteeringInfo
ObjectTemplate.hasMobilePhysics 1
ObjectTemplate.hasCollisionPhysics 1
ObjectTemplate.hasResponsePhysics 1
rem -------------------------------------
ObjectTemplate.addTemplate WillyFrontSpringL
ObjectTemplate.setPosition 0/-0.599/0
rem -------------------------------------
ObjectTemplate.setMinRotation -30/0/0
ObjectTemplate.setMaxRotation 30/0/0
ObjectTemplate.setMaxSpeed 200/0/0
ObjectTemplate.setAcceleration 200/0/0
ObjectTemplate.setInputToYaw c_PIYaw
ObjectTemplate.setAutomaticReset 1
rem *** WillySteeringDummy ***
ObjectTemplate.create AnimatedBundle WillySteeringDummy
rem -------------------------------------
ObjectTemplate.addTemplate WillySteering
rem -------------------------------------
ObjectTemplate.addSkeletonIK Bip01_R_Hand 0.24/-0.1/-0.82 -80/60/50
ObjectTemplate.addSkeletonIK Bip01_L_Hand -0.26/-0.1/-0.82 -80/-60/50
rem *** WillySteering ***
ObjectTemplate.create RotationalBundle WillySteering
ObjectTemplate.setNetworkableInfo WillySteeringInfo
rem -------------------------------------
ObjectTemplate.addTemplate lodWillySteering
rem -------------------------------------
ObjectTemplate.setMinRotation 0/0/-60
ObjectTemplate.setMaxRotation 0/0/60
ObjectTemplate.setMaxSpeed 0/0/180
ObjectTemplate.setAcceleration 0/0/-180
ObjectTemplate.setInputToRoll c_PIYaw
ObjectTemplate.setAutomaticReset 1
rem *** lodWillySteering ***
ObjectTemplate.create LodObject lodWillySteering
rem -------------------------------------
ObjectTemplate.addTemplate WillyHighRSteering
ObjectTemplate.addTemplate WillyLowSteering
rem -------------------------------------
ObjectTemplate.lodSelector WillySteeringSelector
rem *** WillyHighRSteering ***
ObjectTemplate.create SimpleObject WillyHighRSteering
ObjectTemplate.geometry 1P_Willy_Str_M1
rem *** WillyLowSteering ***
ObjectTemplate.create SimpleObject WillyLowSteering
ObjectTemplate.geometry Willy_Steering_M1
LodSelectorTemplate.create DistanceSelector WillySteeringSelector
LodSelectorTemplate.addLodDistance 10
rem *** WillySimple ***
ObjectTemplate.create SimpleObject WillySimple
ObjectTemplate.geometry Willy_Hull_L1
rem *** WillyWreck ***
ObjectTemplate.create SimpleObject WillyWreck
ObjectTemplate.geometry Wreck_Willy_m1
rem *** WillyLodSelector ***
LodSelectorTemplate.create DistCompareSelector2 WillyLodSelector
LodSelectorTemplate.hasDestroyedLod 1
LodSelectorTemplate.addLodDistance 135