It took a while for me to notice, but the master cylinder which came mounted in the engine compartment of the car I am restoring is actually the "later style" which is "incorrect" for the restoration I am doing.  It is this one which is for 240z's from 9/1971: http://www.carpartsmanual.com/datsun/Z-1969-1978/brake/brake-master-cylinder/from-sep-71 The one which was original on my car (6/1971 production) is this one: http://www.carpartsmanual.com/datsun/Z-1969-1978/brake/brake-master-cylinde