From memory (and happy to be corrected)
Mk2 N/a gearbox, with MK3 diff and extended 5th.
Mk2 Driveshafts fitted into Mk3 hubs, build/modify your bearing carrier.

The hard parts are:
Upper rear crossmember needs redesigning for clearance. Access panel for front bank. Hanging the damn thing.

Still, I did my Mk1 V6 long before the jig was available, so it can be done with a bit of patience.