any 1.6-1.8 8v and 16v mk2 and 1.8-2.0 8v mk3 box will be a direct fit, as will most 1.5-1.8 mk1/cabby/scirocco. main worry is some boxes have 90mm shafts, and the really early MK1 boxes dont have holes for the mk2 gearbox mount.
MK2 16v and MK3 2.0 8v will only fit if you change the friction disc for a MK2 16v one as input shaft splines are bigger, but check the box code before you buy the clutch rather than take sellers word for it.
MK3 ABF 16v box will need clutch swap + cable shifter, and either hydro clutch or seat abf/tdi hydro->cable conversion kit.