Chiseling is not good! apart from buggering the nut, you could bend the shafts.
The late Robb Nortier in USA made a series of tools including the castellated sockets. I was selling them here on his behalf. The last of his stock went to Dave Plumb. davmax@ntlworld.com All the clutch sprockets were sold but I don't know what else he has or made. I believe that Mark Cook intends to make some.
Here also is the spring compressor that I made. Ron
thanks for the replies and yes i also think that probably the best option. I guess you guys expect i will be in here again in the future anyway which I don't know is a good omen or not !! I wasn't overly brutal and didn't use a chisel. I had some hook spanner from then chain adjuster of an old VFR750 which fitted a treat but of course only on 1 'castle' so a lot of force on 2 bit. Ill look for correct tools /see if I can make a spying compressor...
Taking clutch domed cover off possibly indicated potential reason for a previous problem i had where clutch slipped a bit under kick stating as there was plenty of oil in there and should be dry i believe. Drawings suggest a cork seal of some sort, I wonder if there's is a potential for a rubber seal/O-ring replacement?