The proof again that you don’t need to do in the complicated to get a nice design. For all those readers who are ready and able to weld-on a simple but still custom gas cap, the Mooneyes Knuckle model is a good choice that will never go out of custom building fashion.
Of course the bung side is in steel with the cap itself machined from 6061 billet aluminum and is available in raw machined, polished or chrome finish. Non-vented or vented is achieved simply by removing the stainless steel set screw on the bottom. Bung (size: 1.4″ x 1.1″ x 2″ high) is included. $250 at Mooneyes USA.