Just my usual 2¢ worth...

The pressure at both ports on any non-stepped bore master cylinder should be virtually identical (assuming no external leakage), except for the instant of pedal application...more in a moment.

One reservoir is always larger on disc/drum masters. The large-reservoir end must be plumbed to the the disc "end" of the car (read: front). This is because discs have no adjusters, the piston slowly moves out as the pads wear, taking the fluid level down with it.

Under normal operation (again, no leaks), the secondary piston the the master "floats" and is applied (moved) via pressure created by the front end of the primary piston. This means that the primary side of the master will have full pressure a few milliseconds before the secondary. Plumbing the primary outlet to the fronts, as on Mopars, will tend to reduce poor-road-friction rear wheel lockup, and partially compensate for the extreme "grabbiness" (self-energizing servo action) of our Bendix rear drums.

Thanks for allowing my drivel...

Rick