A stock Gtir does around 14.2 sec on the quarter and the best mods for them are the same as any Jap Turbo ie FMIC, dump pipe, exhaust, pod filter, ebc set at 1.2 bar, fuel pump, power FC and coil overs should get you started.
The good thing about those cars are that the stock turbo (T28) isnt limited by the ceramic exhaust turbine that skylines are, so you can push them a fair bit harder.
From my understanding all Pulsar Gtirs have quad throttle bodies and solid lifters.