Unless you have a non-vented, threaded screw on gas cap, not much available outside of a race car application to act as a check valve in that 1.5 -2 inch fill line. You can probably pirate one from a salvage yard and a newer car then add a roll over vent valve to your tank such as I have on my '31. Even that will get interesting as there is a very good chance that you will smell gas fumes so an outboard hose with a loop will then be needed. Some condensed gas will then act as a barrier but will still allow the tank to achieve and balance to atmospheric pressure as gasoline is being drawn. Do a roll over and the valve will (hopefully!!) seal. This was a big time factor item for me to figure out, but it works.
Available from Tanks, Inc., Speedway and Summit to name a few.