Use a large pry bar and wedge in between a beefy part of the crank inside the valley (oil pan off of course), then use a breaker bar with proper socket and "lefty loosy". That bolt is not on there very tight. It should not be hard to get off.
If your afraid of using a bar inside against the crank, put a few flywheel bolts back into the back end of the crank and then use same bar across the bolts to hold the crank from spinning (need two people).