I've been told that you can use parts off the later Imps that came with disc brakes. I've also been told you can make yourself crazy trying to find serviceable pieces in a boneyard. You might consider this offering from Speedway.....
http://www.speedwaymotors.com/p/4625...-Size-Car.html
And the correct booster/master cylinder ass'y and prop valve.....
http://www.speedwaymotors.com/p/8302...ter-Combo.html
And these conversion hoses.....
http://www.speedwaymotors.com/p/8300...Hose-Sets.html