Ok mate, in short - the URAS kit is probably the only GOOD option you have for a wide-body look for a 4-door GTT. However, if you with the completed aggressive wide-body look of a GTR, there needs to be other factors you will need to consider to complete the look too;
- Flaring of rear/front guards
- Suitable wheels with good offset to fill guards and bring out tough stance
- A fair amount of custom bodywork to bring the car out more to give you that GTR look you are after
All of the above is assuming you want the GTR look. To answer some other questions you posted, no, a GTR bumper will not fit - you will need to raise your arches and guards etc as GTR's are wider as you already know. No, stock GTR bonnet will not fit, again, modifications to ensure the wider bonnet will fit. The boot will also need to be changed to accommodate the wider rear guards if you want the complete the GTR look. Yes, I believe GTR rear lights will fit as they are the same - but again, if you want to go GTR, the R34 GTR's have only 1 red light and 1 reversing light at the rear. Do your research for R34 GTR specs.
The kit you are after isn't bad and is for sale now locally on Ebay: http://www.ebay.com....e-/130493751164
You should have tried searching SAU, but for more info on a similar post, click here: http://www.skylinesa...-kit-4-r34-gtt/
Good luck.