Some cars have different brake pedals for power/manual with different pedal ratios and direct links to the MC while others use the same pedal and depend on linkage to reduce the pedal ratio for PB.
That's what the Z-bar assembly does - which he's discarding. The Z linkage reduces the pedal travel but increases the pushrod travel. This would usually result in a very stiff pedal but because of the booster it takes very little pedal effort. That's also why it takes so much effort to stop a power brake a car when the engine dies!
