The 3917610 aluminum intake manifold used on '67 & '68 Z/28s has a square boss on top of the coolant runner at the right front corner. Usually stamped on this boss is what I assume is an inspection stamp from Winters Industries. What I find interesting is I have not seen two manifolds with the same stamp. The original intake manifold on my '68 Z/28 is stamped with a capital U surrounded by a circle. The intake from the spare '68 Z/28 engine I have is stamped with a capital V. The attached photo is from an intake on Ebay now, it is stamped with a capital Y. I'm curious, what's stamped on your 3917610 intake manifold?