First off, welcome to the forums! I hope you'll find tons of help here, not many other places to talk to Capri owners who know how to work on their cars.
Wish I could help with it more but I have never needed to go as far as changing pulleys. What I know is that mine was unable to be tensioned enough when I got it, the belt (presumably stock) was just a little too long and I could not adjust the bracket out far enough so what I did was I tried an old belt I had laying around (or did I buy one?) which was a few centimeters shorter, but a few millimeters wider. That did two things. It allowed me to have enough run-out on the bracket to snug it up, and it sits a little higher in the pulleys, but not enough to be in danger of jumping off. Oh, and this belt is a cogged one on the pulley side, don't know if it helps or hurts, but man, it works quietly. The numbers on it are as follows, if it helps:
36017. Made in USA. 3695 : 2