Okay, I'll try to clear this up the best way I know how...
In my experience, there are 3 different 240Z transmission mounts...
Series 1 Transmission Mount, (69-71ish)
Series 2 Transmission Mount, (71-72ish)
and the 73-83 Slide through pins.
The difference between the Series 1 and Series 2 is the actual position of the mount. The series 1 mounts higher up into the transmission tunnel than the series 2 mounts.
If you had them side by side you could also tell the difference. I hope this helps.