Will the work for 4 wheel disc

just to make sure this is clear, the original valve like the one that you pictured at the start of this thread is a distribution block. Since there is no proportioning going on in the distribution block, you can use the old drum brake block that came on the car. I believe that your 71 Demon had a separate proportioning valve (one line in, one line out) about a foot toward the back of the car from the distribution block and the set of lines that you bought should have a line from the distribution block to the proportioning valve and then the longest line in the set goes from the proportioning valve to the hose to the rear axle. With just a little effort you should be able to install the adjustable valve that you have in place of the factory proportioning valve. This allows you to fine tune the system so that the back brakes don't lock up prematurely in a panic stop.