BZs1968firebird my cap looks just like your Mine too is a after market setup. I did check the holley carb that was one of the very first things I did but everything looked great the lines are all dry and the car runs GREAT except for the gas smell. But my vented cap is different than yours but the filler neck is the same setup as mine. I bought my stainless steel gas tank as a kit and maybe the filler neck is for a 400 firebird. I did look at the cap and I am guessing the cap number K630 is possibly a stant gas cap number. I think I saw a cap that looked like yours at pep boys and I will see if its the same number. Thanks for the help