[MrPbody]

Frst things first. Get Jim hand's book "How to Build Max-performance Pontiac V8s" by SA Designs. it will educate you on the ins and outs of the Pontiac.
Generally, all 400s are the same. There are differences. The earlier engines had more compression (10.5-plus). By adding a pair of earlier heads ('67-'70, "large valve"), you will gain a bunch of power over the later low-compression jobs. BUT... Detonation is a very real problem. The pistons should also be "dished" to make a final static compression of 9.5:1, in order to use 93 octane gas.
Lots of goodies to make the Pontiac very powerful. If you describe your intended use, gears, etc., I can make some very specific recommendations. get the book first...