Sounds like you want a later model MC with attached booster.
The original booster, a hydro-vac, is mounted on the frame under the passenger's seat and only works with a single circuit system. possible but not practical to use two for a dual system.
There's no substitution for volume, the wheel cylinders need so much fluid and the only way they get it is with he appropriate bore and stroke MC, residual valves don't give you any more fluid.
Drum brake systems usually have a residual pressure valve as part of the MC or proportioning/junction block, usually 10 lb.
Disc brakes can use a 2lb residual pressure valve if MC is lower than the caliper.
