ND1956Chevy6400,
My bet is always on the head gasket. You can 'read' a head gasket for leaks. If you haven't wiped it off, or thrown it in the garbage, inspect it very closely where any water jacket penetration could have crept through the gasket.
They usually will leave a small track, or will actually eat the head gasket material. You might see a rust track on the block or head too!
If you clean the carbon out of the combustion chamber, you might be able to see inserted seats...they would have a tiny line around them where they were put into the pocket in the head.
Stuart
