Have you tried connecting the pump to another PS gearbox? It's possible there's a restriction of some sort inside the steering gear that's causing the pressure relief valve in both pumps to bypass constantly. You don't even have to mount another box on the frame or connect the Pitman arm- - - -just connect the hoses to it, start the engine, and see if the whine goes away. If so, go ahead and swap it out. If not, keep searching.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!