Any L'Cruiser brake gurus about re:HZJ75 load balancing +Rear Drums

Hoping for some input on a problem with rear brakes on a troop carrier 2-91manuf. Original problem was the escape of the leading shoe on RT-HND Rear set from the slave , creating a jammed wheel. On inspection of all parts the system was found to totally inundated with signs of moisture stress. A complete clean blow-job together with master cylinder and load sequencing valve replacement delivers this new (?) problem, as put here The brake system bleeds normally as in pedal to master cylinder reaction when releasing and pressurizing the system.. When the system is closed the brake pedal reacts normally. On starting the engine the pedal depresses the standard amount. With the vehicle stationary the pedal travel is acceptable. With the vehicle in motion the pedal travel extends beyond 50% and only the front discs are activated on any attempt to brake (measured or emergency). The rear drums appear to have no pressure whatsoever exerted on them. I am casting a suspicious eye at the load sequencing valve, primarily because I do not understand how it works (hydraulic). I am looking for someone to explain the theoretical design of such a contraption :-) In the event I have missed something very obvious I would appreciate a complete jerk back to reality.

thanks.

crusty