The shaft that the pulleys ride on are different sizes for the Federal and Saginaw. The Saginaw was .75, the Federal was .61.
I have several Federal pumps with solid pulleys, they are all about the same diameter. I have one though that is about 4-4 1/2", the smallest that I have ever seen. The only 3 spoke pulleys that I have are on my Saginaw pumps. I've never paid much attention to what is factory correct in terms of power steering pumps, I've just used what fit and what was available.