Power Steering problems

My bro just purchased a '71 Dart. He's having issues with his power steering (jerky movement and wandering steering wheel while driving). He decided to replace the old power steering pump with a new one. However, the pulley from his old pump is pressed on, while the new pump from napa is threaded. This is the non-federal pump he's using btw. So, his question is whether or not he can use a later model pump instead, which uses a pressed on pulley. Is there a pump out there that will work with a PS steering box from a '71, i.e. appropriate pressure? My suggestion was to try and find a federal pump, at least that's what I had on my old '71 Duster, and what I currently have on my '68 Dart. Did Mopar have threaded non-federal pumps in '71? Thanks.

Pumps, their pulleys, brackets, and even the hoses are all different.
Doesn't sound as if the problem was in the pump anyway.
Do we assume the mechanical components were inspected ?
A worn out box coupling, a steering gear loose at its K member mounting, and several other conditions are more likely.

Yeah, he thought he'd replace the pump to see if that makes a difference first. I know, grasping at straws can be annoying sometimes when trying to troubleshoot. When I first saw the car, I noticed the pump right away and figured it was probably not the right one. Which, in turn, could have been causing steering issues. Again, grasping at straws...lol. Thanks for your input.