Ive been doing alot of searching on this Belt length subject with yamaha's. Havent been able to find much. although i did find today that a columbia/HD (OEM # 36394-61) belt may work from '61-'66. but they are about $82-$130.
I did do a search on a belt of the same dims (1-3/16"X38.2") minus appx one inch, and found one at a place called
www.dealsinapinch.com for $31.89 (P/N A-1930V375)plus shipping about $11 to me. i have found some belts out there that are 38.8" long, but dont think that would be short enough to make a difference.
now if i can ever get to it, i think it may work.