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?