FYI, a clean and fully-functional V8 swap is harder in a '63 A-body than in a '64-'66 model. When you go to install one of those screwy bent engines with half its cylinders on the wrong side (and two too many of them), it'll want to hit the firewall of a '63. Changes were made to the '64s specifically to accommodate the new LA V8 engine. V8 swaps into '63s have been successfully done, but be prepared to have to re-engineer the windshield wipers and other stuff.
You might want to consider building a hot Slant-6. The 225's a torque monster; the 170 can be made into a high-RPM screamer. See
here for leads and links, and
here for some racing history on the subject.
