If you just unplug the pump you will have no power assist. The pump pressueises the brake flud which in turn charges that accumulator(the thing that looks like an old time movie "bomb") which is what gives you your power assist. It also helps with the abs too but that is getting way too involved to explane here. I guess you must have legs like stumps to drive without the assist because that pump is the only thing that provides power brakes. It was all I could do to get home when mine went out.
When I converted mine I just got the stuff from another donor vehicle.(93 XJ) I used everything and the swap went pretty good. Had to make 3 lines and mount the prop valve. I had to remove some wires, adjust the pedal rod, ect but it only took like 5 hours or so. The YJ valve will most likely be the same as they had the same brake combo and sizes for both most years.
The prop valve actually doesn't proportion anything its actually a brake line safety valve. This is so if you blow a rear line you still have front brakes. The actual proportioning is done in your master cyl itself. Although sometimes I think that really doesn't matter too much either. My old CJ had large Chevy front calipers and Dodge front rotors for my rear brakes that I made myself. I had the stock 1986 style MC which was for drum brakes and it worked great. I never had any isses with stopping power. If anything I had too much as sometimes it would lock up the rear tires in a panic stop situation. if you need detailed instruction drop me a line. You will need a flare tool which you can rent and a tubing cutter to make a few new lines. Other than that its not really too hard.