Yes, 15/16" was used on the stock power brake A-bodies. But they were backward from the other body styles, E-bodies for example used 15/16" for manual and 1-1/32" for power, exactly opposite from the A's. Has to do with the pedal ratio change going to the power booster, the linkage was different for A's than the other body styles.
Exactly. Its because of the A body power brake linkage being the force multiplier. B, E, C body cars did not have linkages like this, because there was enough room under the hood to not need it.
But since i am going manual discs. The dippy master is sized the same as manual disc brake A bodies. It will be bolted directly to the firewall just like a stock A body cast iron manual disc master cylinder. No multiplier linkages.
Those brackets and linkages were only needed to bring the brake booster up high enough to clear the LH valve cover on a V8 A body, that crazy **** wasnt needed on B,C, E body cars. Since they had enough room under the hood, The linkage from those went straight in from the pedal into the back of the master, or booster in an inline fashion.