I had sold a '99 R1 last year which had a SIGMA slipper clutch fitted. The early R1s (up to 2003) have a diaphragm type clutch spring (not ideal and replaced by coil springs on post '03 R1s), so an early R1 slipper clutch would not fit anyway, and even if you could make it fit ('cos there will be some smart Alec who has the talent to do it I'm sure !!) it would have the less-than-ideal diaphragm spring.
The Gen 1 Fazer clutch has coil springs (as fitted to post '03 R1s) which are generally regarded as much better.
Not sure how the above is at all relevant to this post, but just thought you'd like to know anyway
Cheers,
Fletch