Replacing Federal pump with Saginaw pump?

Welcome, I'm going through the same issues. Decided to change PS pump with minor leak while changing out water pump. Ordered one from Rock Auto, Federal style. Mechanic pulley off the pressed fit pulley off my old one. Went to put the pulley on the new Federal and found the shaft size was different (new .633, old .688) So old pump was a 3/4 hole diameter fit, new one a 5/8 fit. Also back screw hole didn't line up, so had to cut and weld bracket to fit new pump. Tough to find 5/8" pulley press fit. Eventually bought one through Summit (March), aluminum $80. It's 7" diameter vs. old one 5". Had it pressed on. Have to put bracket on and bolt up as 7" is too wide to get bolt through. If I had to do it again (I hope I don't) would go to "counter" Napa, Autozone, Oreilly's and make sure it all matched up. Napa shows one with a pulley/pump combo. Called them, it's discontinued. You may just want to have yours rebuilt. Good luck.