Insurance costs for a piece of equipment like the 4T is cheap and I would think they would be looking at what it would cost to replace the item. If something were to happen to it and it was stolen, what would it cost to replace the item? In this case it would take a lot of searching and transportation to possibly find an equivalent 4T tractor., I agree with Ray54 that the unique nature of this tractor could command a value of $10K. Just my opinion.
Most of the 4T tractors are probably in water graves after WWII. We all just learned that all the 4T tractors and several 3T models were not made by Cat but by the ACF.