Anybody know Ford's, here?

You are correct. Those two pumps are not interchangeable without the brackets they require and if I remember, you may even need different pulleys because of different offsets.

I disagree though that Ford's systems were difficult for interchangeability. In fact,they were some of the easiest there was, because they were more "modular" than the rest. That is of course as long as you stick with the proper brackets for the matching components. Chyslers are similar with the saginaw and federal pumps. Those brackets don't interchange either, so saying the Ford is more difficult is a stretch.