Lining? I didn't know they had a lining? Surely the tanks are just plain galvanized steel? Well, I've fitted two new reproduction ones to my Mustangs and that's all they have been, from what I could see when I peered inside them.
If there is a coating of some sort in your tank then I strongly suspect it was once one of those 'tank treatment' products, meaning that the tank was not in fact new but an older tank that had been 'reconditioned'. ??? It looks very rusty now with some kind of black coating in part which is bubbling and detaching, and the zinc coating which is the protection to the steel has been largely eaten away. Not at all good.
I once tried one of those 'tank treatment' systems - it was a 3 step process - in a '67 Mustang tank with internal surface rust but couldn't be 100% confident of the result. But I never used it as the then-new (this was in NZ in mid '90's) no-lead fuels arriving on the market already had a reputation as being chemically aggressive (numerous owners of older vehicles had problems with fuel lines and carby parts rotting from the inside out, some cars caught fire) so I didn't know whether the proprietary coating would stand up to them. And in any case the tank's exterior - the visible surfaces - didn't look that great (a scrape, a dent, and weathered appearance). So I eventually opted to just fit a shiny new tank, after all it is quite visible at the back. Did the same with my next Mustang.
I think you should ditch yours and fit a new one for peace of mind, it looks pretty far gone. My 2c worth anyway.
