Power Steering Pump

I want to put a new power steering pump in while I'm putting everything together, but I want to get the correct pump. I have converted my car over to a steeroids power rack. All my brackets/accesories came off a 96 f150. I've noticed there is a different pump # for a f15o 5.0 and a mustang 5.0. Just making an assumption the difference is in flow rate/pressure. Should I get a stang pump since it was for a r/p, or go with the f150 pump?

Thanks.
I called Speed Direct, that was pointless. All he could say was that the original mustang pumps were marginal at idle speeds.
I made a couple other calls and found a restoration shop who adamently said to run the late model mustang pump.