On the big trucks there's room enough to mount a regular pick-up vacuum booster that normally mounts to the firewall. All you have to do it remove the old master and make a bracket to mount it to the frame. I used a 1970 pick-up master which had the drum/drum system and mounted it to my booster. I also put a pressure switch in line while replumbing the brake lines, I went 12 volts. Fab up an adjustable pedal rod and run a vacuum line down to the booster and you're done, after bleeding of course,
Scott
