In that case i would think Engine, gearbox, wiring loom, ecu, front engine mount, rear mount on the drivers side i think. Clocks as the tacho gets a different signal for 6 cylinders.
Then other parts depend on if your getting an OBD1 engine or OBD2.
Read up on mk2vr6.com or whatever it is, i know its into a mk2 but its a similar conversion into a mk3 you just dont need to change your sub frame