It seem that i blew a head gasket on saturday , but i made it home ok, I check compression & i had zip in #6.I pulled the head & found what is a crack in the cylinder head on the upper part of the part between the cylinders( see pics).It looks as though its been there a long time & it finally worked its way thru the gasket. I've seen flattys running with alot worse cracks but i'm not too cool on running it again.Its not in the combustion chamber at all. what do you all think ? Also what happen to "Mortec"? is there another site to get ID casting numbers? My buddy has a set of heads but i want to make sure they'll work.There off of a mid 70s 350, mines a 400. JimV PS can't anyone "decode" these numbers?