I just went thru the same sort of problem. I built a custom front disc set up for my 58 Powerwagon. I used 12.5 inch rotors, 3 inch calipers and 1 1/8 power master. I put the power master on there 25 years ago to replace the single reservoir when i built the truck. It worked fine with the drums. However with the discs, the pedal went to almost the floor and the truck would stopped. I bled them multiple times and wasn't happy. So I was thinking the pedal ratio for manual drums are 6 to 1 and for power it is 4 to 1. I had never thought to change it. A faster ratio would reduce pedal travel. It took less than an hour to drill a new hole and adjust the plunger rod. It solved my problem and now the brakes grab better than my daily driver.