How to torque the final bolt on the crank shaft

You can remove the inspection plate on transmission, and lock it down from there, vice grips on the ring gear, large screwdriver...
Roger that.... and you can find a few threads here about damper bolt threads getting messed up with impact wrenches. And I would be leery of what it might do to rod bearings. YMMV on that....

Certainly try to get close to that torque....that high torque is what tightly couples the damper to the crank so it can actually damp the crank vibrations properly.