440 power gains/ aluminum head advantages?

I'm not speaking specifically to any of your questions but it'll speak to them all. Very unusual but wonderful to see someone young whom is pretty deeply engaged in building a hotrod. Pull and sell the dinosaur driveline and put a junkyard Eagle gen3 in it and watch your efforts pay off in larger dividends. You'll go a lot faster for less money and it'll be more reliable. People who know me wouldn't believe I'm recommending this but, in the context of everything I've read here, it's sound advice.
While you're still young. Eventually there will be millions of the new Hemi's sitting in scrap yards. Vehicles are just throw a ways now.