I put KH discs on my '65 S and plumbed a Mopar Performance/Wilwood adj. proportioning valve into the rear line, right under the driver seat. Not inside the passenger compartment, but outside under the floor. It seemed like a nice place to put it, easy place to cut the rear brake line and the floor pan offered a nice hump where the knob hangs over so you can turn it. I had to drill two small holes in the floor pan for this though.
Now I can just stop the car, open the door, reach under and make an adjustment, then close the door and go again.