Pintos were using the gas tank as the cargo floor. 1st gen mustangs did the same thing, but a mustang had the gas tank as the trunk floor with a back seat. Pinto being a hatchback put the gas tank in the passenger compartment.
For a low filler neck you need a good sealing gas cap. Plenty of behind the license plate filler necks have dumped gallons of fuel on a hard acceleration. Yes, those GM A-bodies. This also matters on an off-camber situation for a Bronco. You can have the filler cap below the fuel level.
If you look at the original Jeeps, fuel tank under the driver's seat. That is pretty much the same as what you are looking at. Early 70's IH trucks were pretty close but had a little more filler neck.
I'm looking at doing a bumper fill cap on a different project. That run downhill to the top of the tank gets tricky. Planning on flow, venting, really how to fill the tank. And seal it good enough that fuel doesn't leak out and water/dirt doesn't get in. Bumpers are dirty. Way dirtier than the stock location.