Not sure if this will help.
I put a idler pulley (plastic got melted by a bad bearing) and a belt on during a trip last summer. I replaced the plastic with a steel one. (Since I was traveling I bought the two possible sizes). The steel replacement was slightly larger diameter and caused the belt to be a super tight squeeze! I ended up with what I would describe as a hollow moaning. Once home I planned on replacing the tensioner pulley, but it wasn't designed to be replaced, (looked like it was bolted on but it was pressed in) so I got a new tensioner and the correct dia. idler in steel, the belt was 115 1/2" if I remember correctly, and all was well again.
Sent by wing, prayer & ATT