Belts for a bell and howell mod 253-A projector

I had a similar problem with an old 8 mm projector. The belts were dry and cracked and the film would burn up as it was in front of the hot lamp for too long.
I found an "o-ring" from an old water filter and it worked perfectly. Perhaps you could measure the diameter of the belt and find a matching o-ring to replace it with?
This site might be a good place to start your search. http://www.waterfilters.net/O-Rings.html
Good luck!