Take a look at the drawing for the block and you'll see 3 holes for the starter mounting. top, port and bottom of the starter. Do you still have the ground strap from the end of the starter to one of the mounting bolts? If that has been removed, it could give you the problem you were seeing.
Phil also has a good point about the contact plate in the solinoid. If it's pitted real bad, you'll hear the solinoid pull in but no voltage will pass through the contacts to the starter windings.
Mike
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