If you read the shop manual........and I've posted this till I'm blue....
Go to MyMopar they have them free.......they show you in there HOW TO REMOVE the residual valves out of a drum master. This is to overhaul the master
On my 67, which has 73/ 74 A body disc up front, and Lincoln Versailles in the rear, NO prop valve was needed, and furthermore, in my case, the STOCK 67 MASTER worked fine, gave me good pedal (manual master)