If you want to run a high compression motor and want to use the iron D-ports then your dhoices are 670's, 16's,62's, 48's, 12's, or 13's. If you want to run a low compression iron head motor then find a set of 6
x"s from a 350 Pontiac. If you want to use aluminum heads and run low compression then go with the 86cc Edelbrocks. The lower compression will work better with pump gas and are alot better for a street motor. Pontiacs will run on the street with the higher compression heads but be prepared to use alot of octane booster or mix 104 octane racing fuel with pump gas. I use the 670 heads on my 71 GTO and have to run the timing slightly retarded for street use on pump gas. The choice is yours but overall performance will not suffer with the 6X's and the are some nice hydralic rollers out there that will make a low compression Pontiac run like gangbusters and still be streetable.