My 99 Sierra 2500 350 has them. I just had to get one replaced a few weeks ago.Only thong, Im not sire you have a doughnut gasket. I know my 97 Silverado 5.7L 350 has a taper on the manifold that is made like a doughnut gasket. It can not be replaced. I have shorty headers now, and have had them several years, but Im almost sure the OE manifold a is as mentioned.