Brake Master Cylinder Valves
They are talking about a "residual valve". I have never seen one, but understand it is inside the ports where the tubes exit and that you can pull them out easy with needle-nose pliers. I don't know if they were still used in 1974. The later wheel cylinder kits with the cups on the ends of the springs are supposed to eliminate the need for them. I understand you can buy an external residual valve aftermarket, but why?
I expect you know that you will need a proportioning valve to run rear drums with front disks. You can get an adjustable one for ~$25. If you won't have a power booster, you might want to read up whether a 15/16" MC is OK with disks. You might need a smaller bore. On my 65 Dart, I put a booster and MC from a ~96 Breeze on 74 Dart stand-off brackets. No front disks yet, but I wanted to plan for that someday.