I'm starting page and will be posting pics and info building my 273 commando. This engine I'm using is an original engine with 70K miles on it . Has the oem high compression pistons with a standard bore . I will be installing my closed chamber 920 heads, headers , ld340 intake and a custom grind isky T-3 solid cam that was just ordered 455 lift 260 adv duration. I have a question as this build procedes >>> What would be the difference in compression if I were to use the oem steel shim head gasket at 10.5:1 vs. the mr gasket 1121g Head Gasket; Flexible Graphite Core; Elastomer Coated; 4.140 in. Gasket Bore; 0.028 in. Compressed Thickness .028 thick . Since the bore of 4.14 is quite large for the 3.65 oem bore , I would loose some compression . Can anyone tell me what would be approx loss by using the 4.14 gasket bore .