What are the elongated "U" appearing ports on the intake side of Chevy 396 heads? There are two on each head, one under a 2" rectangular port, and the other on the top of the same port. Am rebuilding the top of this engine, and cannot find a gasket that matches the upper "U", nor can I find an intake manifold that either covers and closes the "U", or utilitzes the upper things. the lower "U" has gasket and manifold use provisions. Have noticed this is the set up, not only in my case, but in many. Photos from machine shops even show these ports, and have painted their blocks with at least gaskets mounted on the blocks, and the paint lines show my situation exactly.