Is the smell really coming from the fuel tank area? If so, I believe the Baby Birds had a real vent in the fuel tank with a tube running around the trunk. The cap should be NON-vented. This car had a full size frame akin with Fairlanes.
So... check for leaks in the tank, around the neck, vent, and rubber coupling. Check the fuel lines along the frame.
Don't forget the short rubber hose going from the frame to the fuel pump. Rubber tends to crack, break, and leak.
A small leak may go undetected. If you smell heavy gas, you have quite a large leak. - Dave