I understand the problem completely. When you get the big block itch, it is very hard not to scratch it!
If you go that direction, be prepared to spend several times what you thought you'd spend. Certainly can be done, but you'll need mucho patience, a fat wallet, and time to do it right. Don't cut corners trying to save a few buckos. Ask the guys here and they'll steer you right. I had a 70 Duster that I pulled the engine and replaced it with a 408 stroker. Excellent running car. Had a '68 Valiant that I put a 440 into and had all kinds of issues. Would not do it again, and did not. Whichever way you go, have fun!