First, having taken a few of these trucks apart, I believe the 1/2-ton conversion bracket would work just fine on a 3/4- or 1-ton. The stock frame brackets the adapter attaches to, if not identical, are very similar.
I used the stock porportioning valve from the 'donor' car when I did my disk/dual conversion. I put donor in quotes because aside from the rear axle and drums I used very little of the brake system from the donor, just specified parts for it when I bought new stuff.
The nice thing about that combo valve is it includes a switch that supports lighting an indicator when the dual master goes out of balance.
If memory serves, the switch grounds when the system is unbalanced, so connecting an indicator between an ignition switched power source and that switch means the indicator will light when the two sides are not balanced.
I would quit reading a publication that argued against converting to dual master on anything other than a very limited use show restoration.
One further thought. Dual master became the standard in 1967. Anything with a single master is now at least 43 years old. Unless you are replacing every piece including the lines with new stuff you are trusting you life and those of others on wear and corrosion prone parts more than 40 years old. And if you are not a good proffesional brake installer, ask yourself if you'd bet your kid's life on the work you've done.
A dual master system dramatically increases the odds your brake system will work when you need it. For me I can't imagine ever doing a truck without a dual master conversion.
