Trying to turbo the RB25DE will give you some problems.
For 1, compression ratio.
2, the engine design differs abit. if im not mistaken, the RB25DET has something like an injector or something for cooling and pushing oil in at the top of the cylinder.
Something to that effect..
Be prepared for a massive labour bill and also if im not mistaken, the gearboxes in the N/A skyline's arent good for much power but... i guess everyone wants his own journey? :)