http://www.moparaction.com/Tech/beep...WN-re-v1.4.pdf
Found this solution to PS pump pressure. The later Magnums put out about 1400 psi. The Mustang II rack only wants about 7 - 800.
I've also seen it in terms of volume, the Mustang rack wanting about 2 gal/min. Later Chevy pumps put out about 3, not sure on the Mopars.