I have the reverse situation on my West Coast Cobra - a Saginaw pump (3 GPM, 1200+ PSI) on my 460 with a Mustang II rack (designed for 1000 PSI & 2 GPM). For me it's simple - drop the pressure with a Borgeson kit and install one of the many flow restriction valves available.
As to the situation described by the OP, it seems the 2 options are: 1) chase down a Saginaw pump and brackets to match the rack; or 2) change the rack to match the pump. I'd be inclined to chase option #1 if it was my car.
Pump bracket:
Borgeson Universal Company :: Pumps, Brkts & Hoses :: Self Contained Power Steering Pumps & Brackets :: Ford 289/302/351W Saginaw P/S Pump Bracket
Pump & bracket:
Borgeson Universal Company :: Pumps, Brkts & Hoses :: Power Steering Pump Upgrade Kits for Fords :: P/S Pump Upgrade, SBF 289/302/351W
It also looks like March's #30037 bracket will work for the pump, but no mention of the pulley required - might be worth placing a call to March.