I could look mine up tomorrow. But if you put a string around and measure and get length and the width can be looked up. Napa or whoever will carry or can get in a day. Alternators are different size pulleys.
I think that the belt is connected more to the engine than to the airframe. I put here a picture of alternator belt but actually I used No. 7355 (not 7360 as in the picture) on my XIO360-M1B (RV8A 4X-OAA)
Ariel Arielly
RV8A #80295
4X-OAA