Can tell you from experience the best way to loosen the crank bolt on any vehicle is to first stop the engine from rotating. Anything you do to remove the bolt will have a much higher chance of success if you can stop [lock] the rotation of the motor when you apply torque. In the past, Ive had luck using (or making) a tool to lock the flywheel or ring gear in place while applying the torque to the balancer nut.
Second - get a big air impact powered by a good compressor. Ingersol Rand or Chicago Pneumatic are my choices. Both of them make 1/2 inch drive impacts with up to 500 lbs of torque. A compressor with a large tank is helpful. Low cfm units with small tanks are useless for this kind of work. Most good 1/2" impacts are going to use 5-8 cfm. Some of those little guys are barely putting out 5 @ 90psi - just not enough. And stay away from the off brand impacts. Sloppy motors. No torque and they use a lot of air doing nothing. They basically just exhaust the air that a good motor will use for power.
I've used the "bump start" methods with the big breaker bar. Works, however, it can be dangerous. Bar breaks, slips off, etc.