How bad does your block look? You can bore an early Olds 350 .100 over, try that on a sbc. You can use 400 sbc aftermarket pistons and rods in your Olds 350. Extend or stretch wires, different exhaust with manifolds and double check your trans bolt pattern. Mounts, battery position etc. I have done the opposite in trucks, some head scratching to get them done.