To do the earlier engines you'll also need the transmission as the bolt pattern between the VG/VE is different than the VQ. You'd also need to make sure the axles match with the 4th gen's hubs.
Wiring wise, my guess is it'll be kind of like the VH swap into your Z. You'll need the wiring harness and ECU and probably have to splice some wires in. If the 95 has CONSULT you'll lose that feature as the 3rd gens didn't have it.
Motor and transmission mounts will also probably be different but the oil pan probably won't be too much of an issue. I bet they're all front sump. I know the VG is, pretty sure the VE is, not sure about the VQ.
I checked out
http://www.car-part.com and found a VQ for 300 up in Dallas. Its a bit of a drive but would probably be worth compared to trying to swap the engine. I just see lots of headaches in trying that swap. You may also just try searching for a VQ block at car-part.com and swap the heads over and such.