Finishing the GTR is not that difficult I think. Doing a Supra AWD is, you might use the Mark 2 (jzx90 frame) as a donor cause it's JZ based and 4WD (1jz-ge I think). A supra is a RWD car, you should not convert that IMHO. A Skyline is a nice 4WD car, a Supra is a nice RWD.