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.
The feel tanks are welded aluminum and may be easily removed from the aircraft (given a little patience and dexterity). The hardest part is disconnecting the fuel lines. I have a few I tunes I can send of the 4 tanks out of the aircraft so you may see the shape and fittings, if you are still interested. Replacements would have to be locally manufactured as these parts are not readily available.