There are five belts in this unit:
The square take up belt that runs from the top of the capstan to a white pulley was about 48 mm in diameter. When I replaced it with a new one of the same size, it didn't work. So, I tried smaller sizes until the take up reel turned reliably. ~40 mm did the trick.
The flat capstan belt was completely melted. It appears to have been about 101 mm in diameter. I didn't have a replacement, so I made one out of vinyl electrical tape. After six hours of testing, it still works consistently.
The loading motor belt was fine and hasn't been measured.
The counter mech uses two belts. The first is ~63 mm in diameter and goes from the take up reel to a double pulley.
The second belt goes from the double pulley to the counter mech. It's about 32 mm in diameter.
There are several date code locations including: the inside of the front panel, the forward/reverse motor, and the top of the loading mech (month & day). As you can see, this unit was manufactured in December of 1982.