I took mine to a very good motorcycle mechanic he tried impact gun & heat torch no joy after one hour
only melted rubber from back of sprocket, I took his advice and took my angle grinder to the nut.
Very slowly & carefully took the larger inner part of the nut down to the same dimensions as the
smaller outer end, taking care not to go anywhere near the threads on the shaft.
Got the nut the same on all sides and it came of with just a socket & 12" bar.
The mechanic I used said it is a regular job for him on Kawasaki bikes the first time the
sprocket comes off, he also said it you can't get it off once the nut has been reduced
use a dremel or similar small cutting disc to score a channel down one side of the nut
starting at the outer end so you can gauge how deep to go to not touch the threads on the shaft.
Once you have a decent channel cut use a flat screwdriver or small chisel to open the channel.Regards
Hope this helps it sounds daunting but with patience and care it is easy ( I did it) so it must be.
Good luck, Harry.