i have a vl commodore i just dropped a rb25det in it you can pick up rb25det half cuts between 2500 and 3000 i got mine with 87 000kms on clock for 2800. its got everything needed from gearbox to wiring loom. i have heard from a stock rb25det with a aftermarket ecu with a good tune you can you get to 220rwkw however the turbo wont last to long. im looking at getting a hypergear atr43 g3 profile turbo which bolts straight up to the OEM manifold and looking at roughly 270rwkw. im also running a microtech lt12s all up i have spent roughly 6k.
be prepared all engine conversions cost more then you think. i learnt the hard way. any questions just ask me seeing r31 is basicly the same as vl commodore in the drivetrain sense of things