Hy Pinch, on a truck as large as yours you would definitely want power brakes, especially if you were going to carry any loads with it. You are correct when you say feeding the two outlet ports of a dual master cylinder into one line to feed the wheel cylinders defeats the safety aspect of the dual cylinder. I think the easiest way for you to achieve dual system power brakes would be to buy a power booster to mount in front of your new dual master cylinder under the floor in the stock location. There are many suppliers of such kits, one note of caution is that these kits are designed for small trucks and the master cylinder they supply may not have the capacity to operate the large wheel cylinders in the rear of your truck. When you purchased your master cylinder did you specify it was going to operate drum brakes? The only other way to do it would be to install a second Hydrovac and possibly get two of a smaller size since the one on your truck now was designed to activate all the brakes on your truck, hope that helps.
