FWIW, a decade or so ago I made a silicone rubber mold of the right 'gill' and cast a duplicate in fiberglas resin. I sawed a 4" hole in the plastic gill to make a door & opening, and duplicated the stock hinge parts in half-hard 2024 aluminum which is springy. I copped a hole in the body and built a 2X volume surge tank that sits below the gill on the end of the right frame extension. A hose and radiator cap run up under the new plastic right gill. So I have a stock L outside gas filler on the left, and a matching outside filler for radiator coolant on the right. It is so subtle a mod that most people don't notice it, and those who do, seem to think it's stock. I did the 'clone' gill primarily because I wasn't sure the whole thing would look or work right. But it has worked fine since 1998 (described in the POCA Newsletter June '98 w/photos) Sorry- this article predates my storing all my scribbles, so I don't have photos in digital form. But POCA has archived many of the old newsletters on their site
Point of all this is, if you can borrow an outside gas filler from someone that has their car 'down' so you see how the hinge was made, you could easily do the same thing for a 'clone' of the stock left side gas filler. The necessary parts are quite simple to fabricate by hand; the only 'trick' thing is a 4" hole-saw to cut a door out of the stock gill & make a matching hole in the body panel. Just a suggestion.