My daily driver is a 05/72 240Z. My "to be sold" one is a 03/71. The oil pans are different in that the drain plugs are in different positions. My '72 (and later ones that I have had/worked on) all have the drain on the aft of the pan sump. The '71 has it on the right (passenger) side. Other "early" 240Zs I have tinkered with have the same thing. I have garnered from the archives here that there was some kind of a corrective change in design and manufacture due to some design deficiency.