BUT does not the pontiac service manual say its a 325 HP 455 with heads with pressed in studs and lower CR?I would believe the Pontiac printed info more than most any other.You know its a 455 YC,you know its a 455 and you know its a 4 bolt block so what does it matter if its a HO?If you had the complete engine with ALL the original parts like heads,cam,dist carb etc which would give further proof of what you have.Threads like this pop up on here from time to time try to to prove what a engine was or is with just a block.The 64 heads are for sure 1970 455 HO which was the last year for hi CR pontiac engines,71s got hit with lower CR.Tom
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