Dan
If you have can do the same with the FT for your 86 car I can probably be of similar service. The tub number suggests it's original rather than a spare, and it would probably have been either one of the cars run by Dave White for Cary and Steve Bren, or a Russ Newman car.
Again, any logs would help fill gaps in my history of RT4s.
Fuel cell i-ds are the definitive thing, but I recognise that they are not the easiest thing in the world to get.
Best
Chris