One wire alternator swap

Hello, recently purchased a 67 Galaxie with a FE 390. Trying to upgrade to a 1 wire alternator. Both alternators I have purchased will not rotate to install the new belt and insert the bolt for tension in the upper bracket. The back of the alternator where the bearing housing is hits the cylinder head and appears the case is 1/4 for inch deeper than the one I removed. Setting them side by side, you can see the difference in depth and they assured me the second one would fit. Ideas? Thanks.:banghead: