I have a 2006 Knight with the ISC 330. The owners manual says two belts, this is not correct. There is a single belt that drives all of the components including the A/C. All adjustments are done with tensioner. I used Napa part number NAPA 25-080830. I would do what @cbr046 suggested and measure the length you need with a piece of string. I would also suggest buying a slightly longer and slightly shorter belt and use the one the fits best when bypassing the A/C. If the belt is too short you will never get it over the tensioner. You can always return the unused belts (at least here in the US).