Peter, there are others more knowledgeable than I, but there are 4 separate 20 gallon metal tanks that are each connected to the fuel selector in the cockpit. It is set up as a main and aux on each wing. The fuel selector is a single selector and has a detente for each tank and one for the Off position.
I am unaware of an approved replacement. I have had a couple of leaks in the past and the tank comes out and goes and gets welded.
Hope this helps. Again, others may have more detail.
Best-
Ed