Just for comparison, I, always low buck, stuck a Versailles rear axle---Ford 9" with factory disk--under my 67, along with the usual 73/74 A body disk setup up front. I just thought I'd try it so I left the original master in place off the 9" factory drums. I ruptured the residual valves with a nail stuck through, and they work great. The pedal DOES have a bit of travel, I'd say about 30-40% of total, but when it hits bottom, it is ROCK HARD
As long as you check the fluid "once a year" there is no need to worry about the size of the reservoirs. The important thing is an optional bore size, and no residual valves.