Used original tanks often have rust issues at this age. The European Ebay often has new old stock tanks. Getting a bit pricey these days. There is a discussion from a while back (3 or 4 years?) of making a tank from fiberglas, from making the form, and a mold, and finally the tank.
'82 and '83 tanks differ in that the '83 has a 'port' for the fuel gauge that the '82 does not have, so not exactly interchangeable if you are trying to keep things specifically original.
