Darn that liner, had enough problems with that years ago. Removing the rest can be a real pita if you don't have access to the right products.
Down there, I'd look up a radiator shop, they may be able to help you if just to clean the tank.
DIY and not tested by myself, apparently good old vinegar will work altough it may take a few days and you may have to toss a few screws in there and shake.Better maybe if you can find cleaning/stripping vinegar, it has a higher acetic acid content.
I sure shaked a tank a lot back then, even drove around with it in the back of the car for days letting the accell/decell move the weighted "Kurly Kates" I had stuck in there.
The filter sock, that's not all that much good at filtering, you may have plugged the pump itself but if it still runs I'd look at cleaning/flushing it first and some bench testing. Plugged fuel filter well....just removed one such from a BMW at half the recommended milleage.Not that good for the pump and now I am worried.
Anyway, quite a lot of info on the net as how to deal with the "Redcoat", lots on here: