lucky man
it looks like you in luck my friend!!
The casing's look identical, but the mounts on the box will need to be swapped for the gti-r one's obviously, the clutch fork looks the same. . .
The only thing i would question, is the amount of splines there are on the input shaft but i cant see why NISSAN would have made them different.
Just hope the gti-r drive shafts fit the diff!!! Take one or both with you when you go to collect, and the clutch disk so you can check the input shaft!!!
If your still concerned that the box will match up to your block, get some thick paper/card and make a gasket to fit between the two with all the holes all in the correct places, then when you got to collect you can check again!!!