Econoline disc brake / master cylinder upgrade

I'm new to this forum but have an old 1964 econoline and have been on here looking at various forums in the past and it has been very useful so thanks in advance. My son has a 1963 Econoline and I'd like to help him do front disc brakes and was looking at some options for the master cylinder as well. I think I could handle the disc brake conversion described on this site but before I look more into the dual master cylinder swap, I was thinking about another option but not sure if it is a feasible... or smart option.

Right now, the single master cylinder has a splitter at the back of it, with one line going to the front brakes and the other one to the back brakes. What if I was to put both those 2 lines into the front and back inputs of a combination valve like the picture shown below. (I know it shows a dual master cylinder in the pic and obviously that is the best option) I know the dual master cylinder allows for a failure in front or back without affecting each other.... but doesn't the combination valve also do that? (I had a failure in a dodge van one time and it was the combination valve so had to learn about how they worked when I was doing the troubleshooting for it)
If in the picture below, the rear brakes fail, then the piston in the combination valve moves to shut off fluid to the rears, and vice versa for a front failure.... so even though in my case, there is only a single master cylinder supplying fluid to both combination valve inputs, would there not still be isolation front and back though it?
I just thought that this could possibly work and avoid the need to do a dual master cylinder modification and then we could also wire a brake warning light to the combination valve as well which would warn of a failure.
Maybe I'm way off on my thinking, and hoping someone here with a lot more knowledge than me, can tell me if it would work, or if it would not.

I got the pic below from:

http://mbmbrakes.com/typical-brake-...Drum brakes require a 10,and sometimes a 2 lb.

And another good video I found was



DISC BRAKES FRONT AND DRUMS REAR WITH MASTER UNDER FLOOR

• disc/drum, under floor

The best way to plumb a disc/drum system when the master is under the floor is with a combination valve (PV2) and then a 2 pound residual valve (RPV2) to the front which is needed to prevent fluid from flowing back from the calipers into the master. We also recommend the addition of a 10 lb residual valve (RPV10) to the rear drum brakes.

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