Had the same problem with a high strung 360 in my car. It once threw the belt off and over the fan without catching the fan( do NOT ask how! Still miffed) i see you have a double groove pulley on the alt. I had a/c pulleys on mine as well, no a/c, so I thought I'd just run 2 belts. It kind of worked, but I did remove my fan and shroud asm and went electric. Much better.