Been doing it for years, you take a piece of black plumbers steel pipe, 5/8's, and grind it down on the desired angle to get back square from the front pulley to the drive pulley- put it between the alt. & the head. The bolt should go about 1/2" into the head, it's only needed to stabilize the top of the alt. from twisting and throwing the belt.
Don't over tighten.