Combination valve ??'s

[deadcarny]

I just converted the car to 4 wheel Disc Brakes from 4 wheel drum brakes. I was told that I could leave the stock Combo valve in place if I gut it out (??) and then install an adjustable proportioning valve in the line to the rears. Is this correct? What harm is there to just leaving the stocker as is? Is it because of the "residual" needed for the rear drums? It is going to be a while before the car sees actual street duty, but it will be moved around for work and the brakes will be used during these moves. will the brakes still work good enough to move it around with the stocker as is and without a prop valve??