SMF and unsprung friction disc?
 

In classic minis, I've replaced spring-damping friction discs with solid, undamped friction discs with no ill effects.

Background-- I'm converting an R50 to 6 spd for track-only endurance racing use.

I'm looking at getting a lightened single mass flywheel (clutchmasters steel is the frontrunner right now for no particular reason than its ~$350 and doesn't have a bolt-on friction surface with what I call cheese grater holes in it) but I also like the OEM friction disc and spring. I'm not sure if the clutchmasters requires their own spring and throwout bearing and so forth, however.

But, in general, has anyone here tried an unsprung friction disc with a SMF on a MINI? I don't mind being the first to try it here. But if someone has a compelling reason to NOT try this other than "smoother shifts", I'm open to hearing it / them.

not here, the valeo singles mass conversion is cheap and works well for me at the track

In my R56 I went with a OS Giken street touring that has a lightened single mass flywheel setup, but has a spring loaded clutch disk. Worked great for me with 244Whp my first year in SMF. Like mega72 said valeo single conversion would probably be your best bet unless your making crazy power.