I wanted to add some more info for the future.
1) The regulator piston that Don posted is for the Saginaw canned ham style pump. Those pumps are ultra common in other applications and are very easy to tune the output pressure on. The output pressure is controlled by the length of the piston. The shorter it is the higher the pressure. You can get new pistons or get shim kits to put shims under the nut to increase the overall length. All you have to do is remove the high pressure line from the pump then remove the fitting from the back of the pump. The piston is inside. Messy job but not difficult. I am no guru on the subject but I think there were some stock 351C applications that used this pump so OEM style brackets are out there but are hard to find. Other options include all of the billet stuff made by March and others.
2) As best as I can tell the output pressure of the ford style pump cannot easily be lowered. I "think" it could be changed by swapping springs (or possibly grinding them shorter) in the pump, but I don't know of anyone who makes spring kits, or if that is even how it works for certain.
3) Steering feels is controlled by a lot of things, but one of the main factors is the size of the torsion bar inside the steering box. If you look at the end of the input shaft where the rag joint connects on the splined shaft you will see a protrusion that is about 1/4" and smooth. This is the torsion bar, it is spring steel and connects to the valve inside the box. When you steer the wheel one way or the other this torsion bar deflects clockwise or counterclockwise depending on which way you are turning the wheel. Once it deflects the valve ports oil to one side of the piston or the other and gives you power steering. The smaller the torsion bar the easier it deflects, and the less effort you have to put on your steering wheel before the assist kicks in. Even if you swap guts in the box for the quick 12.7:1 ratio or go to an original variable ratio box if you keep the same Mustang input assembly you will still have a torsion bar that is about .185", which is pretty small and does not give you much feel. Nothing can change this unless you up the size of the torsion bar. It really isn't a DIY friendly project, unless you swap the entire input assembly for one that has a larger t-bar. There were F body (Camaro, Firebird) GM cars that had .210 diameter torsion bars. I did this swap in mine, the only issue is making a custom rag joint to connect the 30 spline GM input to the Ford column. Also a steering box shop that has the tools can install a new, larger torsion bar in your old box (but I don't know who does this work).
Anyway I just wanted to toss my $.02 in. If you want to change feel you really need to swap torsion bars in the box. Also should lower pressure by swapping to a Saginaw style pump, or using an external regulator.
Peter