The aftermarket unit which is similar to the factory set up uses a Ford control valve. Ford used this system for many years.
GM used it from 55-64 on cars and through 66 on trucks. One of the weaknesses of this system is that it supplements the standard steering box. If you have wear in the steering box or other steering components it becomes worse when the PS is installed.
I installed the aftermarket system with a good front end and steering. It performed well at low speeds and parking but was not at all good on the road.
Fred
