What I would do, is get a piece of string, run it around all the pulleys, and then measure the string. Belt part numbers usually have the length in millimters so you should be able to find a close match. Also, take note of the pulley groove, is it wide, narrow or a deep v etc..I had to do that when I installed an under driven crank pulley on my L28; no part numbers where available so I had to pick a belt off from the shelf. Took about three tries but I got it in the end..