I lost the chrome gas cap that came with my kit so I replaced it with a STANT 11121 oil cap (toyota cam style) and slightly modded it, its a perfect fit.
Amazon.com: Stant 11121 Oil Filler Cap: Automotive
it was at pep boys for 3.99
I clipped a small amount of metal from one of the tabs and drilled a small hole in the top for venting - I also used a wheel grinder to remove the "oil blah blah" off the handle/ridge. i drilled the hole in this part. pics explain all