Whenever you modify one thing you modify everything. You generally can't find non stock stuff in most auto parts stores, if they can't look it up on the computer they can't help you. Try to get familiar with specialty shops. If the steering is still reacting too fast it likely has too much pressure and is unsafe. A GM pump produces about 1300 PSI and the Mustang II operates on about 900 PSI. I have done several of them along with Toyota conversions and have had no problems using the GM pump with the shim kit in the control valve. It is a trial & error process though. Start with 3 shims and try it. You can add or subtract as necessary. Fred

1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine