I have a 69 mach and just converted my front drums to power discs. All of the new brake parts are reproduction of the 70 boss big bearing brake system(spindles,calipers,rotors,etc). I am down to a few things left to install. The original brakes were drums. So I am left with a distribution block. I know that I need a proportioning valve but I am unclear what valve I need and how this installs with the distribution block? Any suggestions, thanks