I notice also the different style of weights on the front wheels compared to the weights I have seen on 81-20-22's. I have a set of original front wheel weights for my 81, have not gotten them mounted yet and they are different from those in the pictures.
Also, wondered if these tractor might have had different pistons so as to burn the higher octane aviation gas? Can't see the military having a separate supply for tractors vs planes. Or maybe, that isn't a big deal and the engines can burn that gas with no problem?
Just my ramblings however, you started a thread that has me very interested.