I've made a number of tools over the years to hold the crank in place. I would take out the bolts that hold the front accessory pulley to the harmonic balancer. Then take a piece of scrap steel (I have a pile of 3/16 X 4" X 8' that works perfect) and cut the holes using the pulley as a pattern. Torch a hole in the center to gain access to the bolt and you're all set. Now you have an 8' long tool that you can bolt solidly to the end of the crank. You're not putting the crank under any torsional strain to loosen the bolt. You can put an 8' pipe on your breaker bar if that's what it takes and loosen the bolt.
This method has never failed for me. It should work especially well with your engine out of the car.
Experience is something you don't get until just after you need it.