Fuel caps - I Need one that fits my application and where to find it.

[74 challenge]

Hi Everyone,

My 74 challenger is currently rocking a flip top fuel cap on it but underneath there is nothing just a wide open gap at the top of my filler neck. I'd like to get a gas cap for it to stop fuel from coming out if I ever make a hard turn or god forbid an accident. Since the fuel system was done there is no vent at the tank anymore so I need a vented gas cap to go under the flip top cap.

Anyone have any idea which one will work?

Car originaly came with a body painted round one that was vented but the previous owner put the flip top one on. If there is no cap availiable I can always go back to the original.