The front sprocket nuts are always a bastard to undo, they are screwed on with Loctite 620, the hardest setting loctite. Bike in gear, chain guard off, piece of 3 X 2" timber through the spokes of rear wheel and across the top of the swinging arm to lock the rear wheel completely, socket and the longest torsion bar you have and swing on it, get a friend to support the bike to stop you pulling it over. In the end I had to take a hammer and blunt chisel to mine and drift it around but even then it did not give up easily.
Good luck