Well... your clutch springs were ground off because your flywheel was standing still while the crank shaft was spinning the nut that the ends of the springs rest on. If you ran it long enough to do that, your flywheel and/or collet are both probably trashed as well.

To get a crank nut off that is siezed with a flywheel that spins, there aren't a lot of options.
One way is to pull the engine off and take the backplate off, then stick a tooth brush beside the crank shaft inside the engine so it can't rotate. (probably the safest)
Another way is to take the engine off, pull the glow plug, rotate the crank until you see the piston go about half way up/down (until it covers the exhaust port). Fill the glowplug hole/cylinder with ARO and put the GP back in. This will hydrolock the engine and should let you break the nut loose. This will put a lot of stress on the con-rod though.