went through this yesterday and what I found was that if you want to upgrade your earlier clutch you can. the '02 clutch has a thin washer between the basket and the drum and a flat back to the drum. this brings the drum up nicely to the point where the circlip is added.
however, the '03 has a pair of 'C' washers that slot into the gearbox shaft and they get capped by a cupped washer that keeps them in. the '03 hub therefore has a recess in the back of the drum for this thicker set up. after this it is just the same as far as fitting goes.
the next difference is that the teeth on the drum are taller on the later clutch whilst shorter on the basket teeth. the later basket has teeth like a 'pitch fork' while the earlier basket has teeth that have a circular drilled hole in them.
to fit the '03 tubes drum appears as i say to be easy and all the plates fitted spot on in a mock exercise. however, like all the later clutches, the last friction seems to come really close to the top of the basket's teeth.
I expect I'll try and do an upgrade and see how i get on....
regards
Taffy