Do you still have the flywheel on the back of the engine? I ran into a similar problem and used a large screwdriver and a bolt threaded into a tranny/engine bolt hole to brace the crank in place. Just put the tip of a screwdriver/prybar in the flywheel ring gear while the screwdriver/prybar is braced by the bolt. On my truck a high powered impact wrench(400 foot pounds of torque) wouldn't get the front crank bolt off, but holding the flywheel as above combined with a friend and cheater bar got it off.
