They made 2 or 3 different decks for these tractors.
If you can't get any of the model #, measure the width of the deck. Should be either 38 or 42 inch. They might have made a 48 inch that fit also. I can't remember. From there I can try to find the parts book and look up the original belt #, and then the dimensional info for the belt.
This place here can get you just about any Bolens part you need. They also have service manuals, parts lists, and operator manuals available to download for free.