I agree with Ian, it's not as simple as finding a donar car and swapping
Probably an easier way, though maybe not the cheapest, would be to visit
www.mantapart.com They specialize in J-body and N-body performance
modifications, and sell rear disc convertion kits. If they are feeling
nice, they may even know of a donar car. If anyone does aside from GM,
it's probably them. Check that out first, before wasting a lot of time
on a donar car that may not exist.