The length and the width of the belt are what you need unless the Yanmar belt still fits the new alternator correctly. Then if you can find an autoparts store that will help you through the size instead of part #, there may be some options. I've settled on a Gates cogged belt. I think it's a power stripe but I'm not sure. I used some other models that were too soft and stretched easily. This belt is a vast improvement.

I went through a shredding problem with my high output alternator. Part of the problem was alignment, the rest the belt. These alternators are hard on belts so everything needs to be well tuned.