E30 Zone

I recently did a timing belt change on my 1989 e30 325i . Whilst changing that I replaced the waterpump and the alternator belt. Unfortunately the original pulley failed after I put everything back together so I had to find another. Ended up buying one on ebay that came off another e30 but it was a 323i.Anyway it fitted and I put the belt back on,adjusted the alternator,however this time I noted I had to extend the adjustment to its full extension. Result was a couple of days later the belt had popped off.Now iam guessing its one of two problems,either gsf gave me the wrong belt ( AUXILLARY DRIVE V BELT 10x965) or the pulley is a slightly different diameter.
Anyone out there got an idea what iam doing wrong??Any help would be greatly appreciated.

965 is correct for a 325i.

Cheers Brian.Those 3 tourers aren't all yours are they??

Those three are just a sample for the photoshoot. Red one is now sadly deceased, after an encounter with a flying porker.