mk2 gti box fits, but you need a different clutch kit if its an 8v box. 16v one is a direct fit, but 5th is quite short so you'll run out of revs when you get to 120mph and cruising on mway will be a bit more buzzy. the rest of the gears are tighter than the mk3 gti box as well.
trouble comes if you have a later mk3, as they use a different flywheel. if you get a mk2 8v box and you have a late mk3, you need to buy a late mk3 1.8 clutch kit. with the earlier mk3s you just buy mk2 8v clutch kit.
you can tell the difference by checkign the flywheel, the early flywheel has 2 locating dowel pins, the later ones have just the 1. also while on the subject of the dowel pins, make sure you line these up with the pressure plate properly, otherwise you'll damage the pp when you try to do up the bolts
