Bill, I was very gratified to hear your comment about wanting a significant number of operable tank cars. Historically the railroad tended to move blocks of cars, not individual cars, and having multiple examples helps make things like charter trains much more historically accurate.
At the same time, I was pleased to see the C&TS including a "per diem" charge when charter operators use historic equipment, as a way to help raise money for their maintenance.
I think your idea of a "production line" for a specific type has a lot of merit, and would certainly provide me with a good reason to spend some time in Chama or Antonito.
JBWX