You can slide a GTR, but unfortunately, the way the physics are on this game, you can't drift anything 4wd properly, they just don't handle right. My RL R32 GTS-T has GTR arches and a GTR engine with kit/wign/carbon bonnet etc, and I too wanted to copy it in the game, but I'd rather have a car that doesn't look quite right but handles like my car (R32 GTS-T), over a car that looks the same but handles like ****e (R32 GTR).
I know it's not the answer you want, but until the game offers us the opportunity to convert GTR's to permanent RWD, it's the only one you are going to get.