I've got a set of Vortec heads and a set of Hedman 68460 coated longtubes. I'm trying to figure out what header gasket to use with the two. The Hedman's have a round port and the Vortec's have a port that is somewhat square with the corners rounded. I'm sorta confused as to what the gasket manufactures are calling a D-port and a square port. Can someone explain the difference in the two and tell me what gasket I need?