I was able to use my orig gas cap but it needed an extra rubber gasket to fit tightly on the repro tank. Also the repro tank (I think aimed at Camaros) does not have the nipple on the fill neck needed to attach the vent hose to the metal tube that goes up into the trunk. I was able to braze on a metal hose nipple that I cut off an old sending unit. The metal tube is available. I think I got mine from Inline Tube. Came out really nice.