I'm thinking it's the smaller capacity, lower powered version of the range.
It's an interesting comparison, but there are other ways of looking at it too. Personally I'd point more specifically at the 'Z-Std' no frills, base model S30-S Fairlady Z as a good comparison for the 912, but the
somewhat dumbed-down and softened-up north American market HLS30-U Datsun 240Z with could be in with a good shout too.
Don't forget the fact that there were 2 litre 911s too, and that the
unicorn-in-the-room fastest, most powerful, best-equipped and arguably most sporting S30-series Z from launch in 1969 through 1973 also had a 2 litre (but twin cam) engine....
I've been a 911 (and 912) fan since I was a boy, and I'm happy that Nissan took such inspiration from them when they were working on the S30. My favourite Z, the Fairlady Z432-
R, was wholly inspired by the 911-R.