Did some more on my clutch. I had noted that the basket friction lining was quite loose on its rivets but I wasn't too worried because they are held captive and the lining can't really go anywhere. However the consensus seems to be that this is not a good thing. Then I realised that this state of affairs could contribute to clutch drag, if the lining can lift a few thou and chase down some of that precious clutch lift. The final factor that swung it for me is that I worked out that there is a second identical friction lining attached to the back of the basket/sprocket assembly and this too was free to flap around.
So I ordered up new linings and rivets, plus a new primary chain for good measure, and set to work. The old, loose brass rivets are easy to get out if you are patient. I punched them enough from the backside of the basket so that they jammed in their holes then I skimmed off the peened over flair with a drill. Then I could push the rivets out. Some required two punch and drill cycles before they would let go.
Not wanting to suffer loose rivets again (which I think would be inevitable) I decided to JB Weld the linings to the basket and set new rivets. The only disadvantage I can see is that I can't replace the linings again if they wear out. However, the old ones had no discernible wear at 15,000 kms, so the rest of the the clutch would be almost certainly shot by the time I would need to do that.
Right now, the JB Weld joints are curing under load from my valve spring compressor, which makes a handy G-clamp, so I can't yet speak of a successful outcome.
This clutch design has a built in contradiction. It turns out that the basket/sprocket assembly is effectively your fifth lined plate and the extended rim of the main-shaft hub works as your last plain plate. However, the rear lining of the basket also functions as a thrust bearing - so do we want it to slip or do we want it to grip? The problem is that it will always be in contact with the hub when the clutch lifts because the basket sags on its ball race. I think that RE would have been better to confine its function to that of a thrust bearing and make it of smaller diameter and in bronze. The small contribution it makes to clutch grip would be lost but I would trade that for cleaner clutch lift.