ok heres the deal, i have a chevy truck that has what i think is a 76 500. I am currently removing the heads to have a broken exhaust manifold bolt removed. The heads are cast with the numbers 1602493, 500 right? Well there in the cylinders sit true flat top pistons. From the research i have done that means it is a 74 472. Is this true? I hope not... Thanks for the help!