filler neck modification

If you are a fabricator, I would cut a metal disk the same size as the ID of the filler tube (so you can wiggle it in there past the rolled edge) and cut a fuel nozzle size hole so the top is very close to the top of the disk and weld it in there (off the tank of course) That way if some fuel backs up, itll hit the dam you just welded in there. Or just hold the filler sideways or upside down.