i think anDru's input is the best, probably best going for the east bear kit from powerplay however as he said it is rather expensive
in terms of what ive read about this in the past the actual gtr front bar is wider (due to the wider guards obviously) however can be stretched somewhat and put on, i dont know if the guards will just swap over and fit perfectly, also the bonnets for the gtt and gtr are the same dimensions however the hinges and latches are different, the spoiler wont be a problem but not sure about genuine gtr side skirts or rear bar, if your serious about it might just be best to go for the east bear ones
there was a guy a while back on here who bought all the genuine gtr body parts from nissan and put them on his yellow gtt so it can be done
good luck and hope you get the results your after without blowing too much coin