GTR's are fat little bastards.
the bar will fit fine on the front, however where it goes around the sides to meet the gaurds, the gtr has wider guards so it doesnt curve around as much, the gts-t has less wide gaurds, so it needs a 'slimmer' bar.
if you do call fibrevision, just be careful that the bar does actually fit a gts-t.
i bought a bar from them that was supposed to fit a gtst, but the mould was from a gtr, so while the fibreglass flexed and the top could be made to fit, the bottom flared out, looked U G L Y!
when i took it to a shop to get fitted and painted, it was actually cheaper for me to buy a whole new bar and start again, good way to waste $500.
(this was the apparently the case with all their gts-t bumpers, moulded off a gtr which was supposed to be a gts-t!)