Hey dude
R33 GTR original parts can replace the WHOLE front end. I know some people use just the bumper, but it wont give the wide look your after. I believe you will need all parts that make up the front end of the GTR ie guards, front bumper, reo, lights, and bonnet, maybe even the bonnet hinges.
As for the rear end, R33 GTR 4 Door was made by Autech, the rear 1/4 panels and doors are custom. I think a guy named Ernest Parry once did a 33 Sedan to 33 GTR sedan conversion. Apparently there are a couple floating around OZ.
If you want it slightly wider and subtle, the best i can suggest is custom hand flaring/pumping of the guards, that way the amount of extra width is up to you and you can also fit wider wheels (as opposed to "bolt-on flares"), probably cheaper than sourcing Autech parts too.
cheers
Evil