measuring and finding a shorter alternator belt?

I've had to modify the alternator mount slightly on the volvo engine to fit between the s10 frame rails...

I have the stock belt measurements/specs (thank you napa) but I need to know how to measure for the shorter size, obviously a string is the best way to go but do I measure the inner most portion of the pulleys or the outer edge of the pulleys?

know we have some parts house guys here that would prob know so you are my go-to guys :)

please LMK thanks mark

measure in the grooves

awesome... makes it MUCH easier :)

take the belt you have, make a cut in it, and use that to figure out how much shorter you are going to need. you will need to put the tensioner to about where you want it to ride and hold it there, but it's not too hard. if you have a connection at an auto parts store that "gets" what you are doing, they might let you take a few belts at a time without charging you to let you figure out which one you need, then only charge you for the one you actually use. then once you do figure it out, buy a spare and keep it in the trunk.

take the original belt, cut it straight across the width, route it over the pulleys along the new routing, mark the overlap with a sharpie, measure the marked length, win.

thanks for the thoughts guys... will get it taken care of prob next week