[Walt Fricke]

I believe that as the amperage of the alternators grew, the alternators themselves grew in length. Which required that the fan housings be machined deeper, so the pulley would end up over the crank pulley. As long as the fan diameter and the housing ID are right for each other, it is this alternator depth mounting which needs to be adjusted. And the casting numbers on the fan housing aren't a whole lot of help, although I think the shift from 901 numbers to 930 numbers may at least be a way of knowing what for sure is not going to work (unless some machine work was done for longer alternators, or you are willing to shim up a shorter alternator in a housing bored deeper.