it's an RB23DETT which Nissan made only 1 of.
Nissan originally planned to release the R32 GTR as a 2.3 litre and started producing the engines but after the 1st one was built and tested, the engineers decided it needed 2.6L capacity. This lone engine was a HOT commodity in the early 90's and JUN decided that a stroker kit was in order so they built it up.
This is a true collectors item