when I got my BM it had this on the tank, maybe it’s something like this your after ? Just looked like clear vinyl cut to shape, I wasn’t keen on it tbh so changed it for a more conventional Protector..
Perhaps yer being Too 'Precious"? My 81 has Original tank/paint work. Yess.. a bit of Patina.. but nothing visible from 6' away. It's worn a helluvalot better than I have Stop obsessing and ride the thing.