Brake emergency

Air in the system especially a "single" MC system is NOT going to cause different pressures through the system. Air IS going to cause a low, spongy pedal. I didn't notice you mentioned that? Pedal high? Hard? (A low hard pedal is usually shoe adjustment)

Another probem MANY guys miss, not being used to drums, is the SIZE of the drums due to wear or "turning" If a drum is turned or worn very far larger than "standard," the shoe fits inside the drum "in the center" that is the shoe does not have much contact. This reduces the braking area. You can have a nice hard pedal, but very poor braking with this condition.

I'm not sure what your problem is.......have you tried to adjust the shoes and drive the car? ALL shoes must "seat" for a short drive.