gts4's have same body as gts-t's and gts's im pretty sure...the gtr bar would have been a copy as a genuine gtr bar does not line up on gts-t's etc..you will need reinforcement to suit a gts-t or gts-4...just search on the forums for anyone whos got parts they should come pretty easily or wreckers, ebay etc..
if you have a look at "nisswreck" on nissansilvia.com (not sure if theyre on here) they might be able to hook you up..
i had this same problem with my rear bar, parts were fairly easy to come by..
hope this helps