1st, I know that the devil is in the details.... Cam plays a part. Use plays a role. etc. I am looking at head gaskets for a 547... 4.5 bore/4.3 stroke A-headed engine. Flat top pistons and 79cc chambers. I have some SCE copper gaskets on it (.072), but that is about 12-1. Cometic has some thicker gaskets, but I don't want to go any thicker than I have to. Use will be street/strip. Mechanical roller, carbureted, naturally asperated. What is the maximum C/R I might get away with pump gas (93)? How much overlap is required to keep 12-1?