I agree with the premise of a failed master cylinder. Unbolt from the front of booster. Leave the lines attached. Pull away from the booster and see if there is fluid in the pocket at front of booster and is wet at the back of the master cylinder. If doing a 2 person bleed, put a small section of 2"x4" wood at the floor so the pedal cannot go all the way down to the floor.
By the way, you never said why you replaced brake components to begin with. Was it for the pedal feel problem?
By the way, you never said why you replaced brake components to begin with. Was it for the pedal feel problem?