Using 670 heads on a 455 will result in about 12:1 compression. This is WAY too high for any "pump" gas. 110 ONLY. Unless a "race car", not a good choice.
Milling .060" off the current 6X heads (or are they 6Hs?) will get you CLOSE to 9:1. If 6Hs, find some 6X-8s... 6Hs can't be milled "enough" to raise the compression without compromising the intergity of the head's "deck surface".
In lower compression engines (under 9.5:1), we use Comp XE cams. For the 455, XE274H is a good choice. It offers good power and a fairly "broad" band, as well as a "hint" of a lope.
Very important: Before buying ANY parts, consult a true Pontiac "builder" to assure the combination is good. More Pontiacs have been abandoned or blown up due to a "bad combo" than any other reason. Each of us has our own "approach", so "mixing" builders' advice may not be a good idea. Pop always said "Pick a horse. And RIDE IT!"
There is nearly an unlimited amount of modifications that CAN be made. The '76 block should be kept under 600 HP, though. It's the "lightened" version (less iron).
