I once hung a Chrysler alternator on my Datsun to run stuff cause it had more amps and was shorter therefore sat out away from the block farther. On the GM alternators I have very often indexed the rear housing to clear all sorts of things sticking out of the block. Have you tried that yet? If you don't know what I mean, you can unscrew the four long screws and rotate the main case of the alternator so that the bumps, wires, plugs etc point in different directions to clear brackets, exhaust manifolds etc.