1972 duster power brake booster

Disc brakes require about 50% more operating pressure than drum brakes. That can be achieved in a couple of ways. Going to disc: larger booster or dual booster; smaller m/c.
Note that a dual booster may not output anymore force than a larger single booster. Sometimes dual boosters are used for space reasons, NOT because they output more force. The area of the respective diaphragms would need to be calculated to compare output. Also, the dual booster piston/rod does not travel further; one diaphragm is piggy backed onto the other.