My 1997 2500HD with the vortec 35O has them... I had just replaced the intake gaskets last thanks giving... Myself. There are two ports on each head front and rear on both the drivers side and passengers side. Mine was leaking slowly between one of the intake ports and coolent ports.at the back of the block. Eventually it blew out to where it was leakinO on top of the intake. But then again what do I know.