What's he smokin? Putting a small block in a car that arleady has a big block, most people put Big blocks in where small blocks were so really, it's like going backwards. The .60 over 350 would have moderate cooling problems with out a blower, with a blower I'd be even worse problems. If you really want the car, tell him you want the 454 and that's the only way you'll buy it, you may need to put a non refundable deposit on it to make it a done deal, so he knows you won't back out when it's almost done and have to redo things so the blown smallblock will work.