I will tell you that Ford did what Ford wanted to do. Parts interchangeability is a nightmare, and I can say that since I own a T-Bird and a Mustang. The best thing to do is look at the old pump and buy a new one that looks the same. The parts stores are pretty good (but not perfect) about posting pictures of the correct parts, especially for something as popular as a Mustang. I just was looking at pumps for my T-Bird, and the options are NOT the same. I imagine it's the same on the Mustang.
Here are the options for the '65 Mustang at O'Reilly's...
https://www.oreillyauto.com/shop/b/...ing-pump-12580/3d51bc7abdc5/1965/ford/mustang