Lynn (LATECH) knows his Pontiacs.
If the heads are "64" castings (the only casting on '70 455 "HO" engines), they were quite populaqr to use on 400s , as they drop compression to about 9.2:1, ideal for modern gas.
NOTE: '71 and '72 "HO" engines had round exhaust ports. The '70 did not.
Pontiacs with stock "cast" connecting rods will sound like a "tap" when a rod bearing is knocking. It can be deceiving. When you put your list of parts together, be certain to include new connecting rods (RPM forgings are the best buy, IMO) and a balance job.
To learn more about the ol' Injun, get Jim Hand's "How to Build Max-performance Pontiac V8s" published by SA Designs. Though a bit dated, it is the most current and accurate information available at this time.