I'm trying to understand this John because I didn't have a problem. The bellhousing is the Datsun part that you keep so why is another threaded hole needed if it already has one for the reverse switch?
There are at least 3 different bell housings, 2 have different positions for the reverse detent rod switch, one works with the S14 (the later 280Z one) the other (the earlier 240/260) doesnt.....its as simple as that .....been there done that.
It can be overcome by welding and drilling a boss, buts its an extra faff.
Then theres the different speedo drives, ones an aluminium body the others steel, one has a slightly greater "cam" offset than the other so engages better with the worn drive.
I guess nearly 20 conversions lets you aquire a great deal of data that others may not see or will overlook.