the GTR bush should be the large one.
So if it's a GTR box, the smaller bush should not be able to fit the GTR gearbox.
Failing that, take both bushes off and try to swap them, if the larger bush will not go on (requires a lot of force and you need to pop it in at an angle) then go down to your local nissan and buy the RB25 shifter bush which should fit directly (but it's larger like the GTR one so I don't know if you are going to run into trouble there.
I still can't get my head past the smaller bush, it shouldn't have a small hole in there in the first place