The best way to pick a power valve is to watch a vacuum gauge that you temporarily hang in the cabin while driving. That way you can tell exactly when you want the extra fuel to come in. I would guess you will end up with a 10.5 - 12.5 with as much vac as your engine has.
Two 1970 and later style square back alternators. I have not had them tested, so consider them cores for a rebuild. $50 for the pair. Pickup in west central WI, 100 miles straight east of the Twin Cities.
I run PST's 20:1 boxes in both my B-bodies, but in my lighter 70 Duster I have their 16:1. I think it is perfect in the A-body. Just something else to think about.
Two 1969 and earlier style round back alternators. I have not had them tested, so consider them cores for a rebuild. $50 for the pair. Pickup in west central WI, 100 miles straight east of the Twin Cities.