Good tip which has proved sucessfull over the past few weeks for anyone who has a late primary chaincase with the clutch spring adjustment hole.
As its crucial to have the clutch plates lifting nice and squarely I used a tyre depth gauge. It was only an experiment and I didn't expect it to work because the clutch basket/drum has a slight wobble. However I have had the last few weeks with the smoothest clutch operation. I've been well pleased!