Mechanically, there is no difference between a series 1 and 2 R33 era RB25.
Things like ECU, coilpacks, TPS are different (and thus the harness).
RB20 & RB25 exhaust manifolds are the same.
RB20 and RB25s1 coils and igniter are the same (s2 went to igniters on the coils), RB20 and RB25s1 AFM is also the same.
Use the P/S and A/C that are already in the car, should all bolt up to the block fine.