The Z-bar is only to be used with cars with power brakes. If you use it on manual brakes, you will not have the energy/strength to press the brake petal down.
Sense power brakes are, well, power assisted, the Z-bar allows that power assist to allow double movement of brake petal (sense booster is assisting you with petal movement).
Adding the Z-bar also raises the brake booster up on firewall up 1½ to 2” – which is why the brake firewall support plate is needed (high for booster or low, without booster).
You could use power brakes without the Z-bar but petal movement would be twice as much as usual.
A side benefit of Z-bar is it raises brake booster up and away from engine more so.
There should be a rubber square cut O-ring or sleeve that goes over the end of master cylinder rod to keep it retained in the brake master cylinder.
BudW