you will barely have enough room to shoehorn a 350 let alone a big block. i was about to pull a 500ci from a early 70s caddy for my mk3 before i realized the exhaust would have to go right through the fender well just in front of the door. it kinda took away from the sleeper look plus the weight would have annihilated the entire front suspension. there has been success with LS series GM motors which is what i got sitting in my shed. here's a link to a build i have been following for a very long time. SySt's Build up - SupraMania