nah leave as NA dotn turbo it! it will cost you arms and legs!
if you want put RB26DETT depends on the price of the GTR engine.
If I knew you early I would have sold my BLITZ ECU and filter etc..etc. too late now.
only you can do is go raicey, Performance is out of the window with NA skylines.
jsut get decent sound system and body kits, you can do some engine mod but not much...
cheers
JOe