I think we are talking about the same subject.....I'm just at the end of the coolant flow study by mentioning the last gasket used by GM.
Maybe GM never did much coolant flow work on this engine.Chevy introduced the inline 6 in the late 1920's and then it changed over the years into the 235-261 engine.If the original engine cooled ok right off the drafting table them that might have been the end of it.
216's and many other engines have cooling tubes in the head.This is expensive to manufacture compared to a hole in cast iron.Surprising that GM being as cheap as they were at times didn't get rid of the tubes form the original design.
