The disk brake kits I have installed came with adjustable proportioning valves. I could be wrong, but I think that might be what you want. The combination valve you linked to does not appear to be adjustable. How do you know the force distribution will be appropriate for your application? When a manufacturer put disk brakes on a car back in the day, I'm sure the engineers had worked out the exact force distribution needed, so an adjustable proportioning valve would not have been needed. There are so many possibilities on disk conversion combinations today that I think an adjustable proportioning valve would be the safe way to go.
