Only if you've got the right bellhousing to mate to the rest of the gearbox. There were 6 different bellhousings for the Series II/IIa/III boxes.
If it's a series III you're alright as there were only 2 bellhousings,
2.25 and 2.6. The only bit you need to be aware of is that behind the bellhousing there is a distance piece on the layshaft which sets layshaft endfloat. This may need to be changed for a different thickness if the bellhousing is changed.Alex