Brakes again

A year later and I still have a brake problem..I visited a local Z mechanic and he said I have the wrong master cylinder installed. Because my Z was built in July of '71, he thinks it uses the '72 model of master cylinder. He claims that some of the later '71s actually are '72s. I find that hard to believe. Anyway..I bought another master from him (for a '72) and when I looked it over I noticed the end that the push rod from the booster (Master-Vac) is a very deep recessed "V", whereas the one I have installed is a shallow cup. This obviously would be affected by how far the pushrod will seat into the end of the master. My "new" booster would have to have the rod readjusted from ~.15" to ~ .39" from the front of the mounting flange. Something is wrong here! Not only that, the way I read the manual, the front and back braking is independent of each other and the larger reservoir goes on the front brake section, but it is marked towards the back of the master on this new one. Anyone out there really knowledgeable about this?Thanks in advance.