well quite a bit! vr6 syncro gearbox, front driveshafts, prop shaft, rear drivesahafts, rear diff, syncro rear subframe and arms, modify rear boot floor/buy mk3 golf syncro rear floor+rear cross-member, syncro fuel tank/or custom ali tank, modify centre tunnel with brackets for prop, i think thats about it!!! i`m in the middle of a similar project but using o2m gearbox and running gear off a mk4 r32-lots more modifying, blood sweat and tears!! can i ask why your thinking of converting to 4wd?