These machines used the Comet TAV 30 series system. If this is the original TAV, it likely has the 2 bushings/washers used to space the moving sheave outwards a bit. Do a search for Certified Parts Janesville WI and this company purchased the Comet assets and produces genuine USA parts now. They also have the manuals you can download on-line.
Note that this is the original TAV series 30, not the later TAV2.
There is only 1 belt model number for the TAV. If you cannot locate the number, PM me. I just supplied two of them for a friend.
I have one of the Monster Jeeps under restoration now.