I am switching to rear discs on my 92 GMC 1/2T. I wanted to get a new master cyl set up for discs. Instead of just a proportioning valve. I had heard that a master and booster out of a 92 3500HD with disc would fit. However mine is vacuum and the 3500HD is hydrolic. That means to much swapping for me. Does anyone have any ideas or know of a vacuum setup for 4wheel disc that will fit my rig?