Found 2 suspect items in the clutch.
The spring disk behind the clutch centre (you know the part that's fit and forget) was in back to front. Must have been like that for years as I didn't remove it on the rebuild. Its the one behind the giant circlip that never needs replacing, weird.
Also the adjusting bolt threaded end that goes through the lever pivot was bent. I have a spare one of those, so fitted that.
Just waiting for some new 25mm circlips as it bent getting it out, and a new gasket. Then I shall give it another go.
Everything else is where it should be, and the disk stack measurement works out correct according to the manual.
Will see how it looks when it's back together.
Thanks for all the comments and help again.