These were Duralast 15610's. I don't know who makes the belts for AZ, it wasn't clear on the band. This is a bit longer than stock 70 383 with a/c because I'm running a GM case alternator that is swung out a bit more to clear the head. These belts are a touch wide to sit into the grooves as nice as I'd like but I think that is the price paid for the longer belt.
It was _ok_ without the a/c on, but 1 really flopped with the a/c on, and it kicked that belt when I went racing last month. Been running with just the 1 belt but it has started to squeal some with the a/c on, can't hold both it and the alt drawing power for the EFI ecu and fuel pump apparently.