How about unplugging it, then putting a bypass valve in the pressure line that is hooked up as an 'H' with the return line, and an adjustable petcock on there to bleed off some off the assist ?? I remember seeeing a magazine article in Super Ford magazine about 10 years ago where they did that on a late 60s Ford vehicle to try get some more steering feel out of it.
cheers
Ed Nicholson
SCCoO