You are 100% correct.well, at this point you really only have 2-3 options
find or make a tool to hold the crank in order to achieve your 200 ft lbs. of torque and give it another try
get a new crankshaft
lot of dynamics at play right there. torsional, vibrational, heat, etc. it's a 6200 cc beast that's propelling a 5-6000 pound machine and turning a bunch or accessories. the keyway and key can't have any slop at all
That's why that key is strictly for alignment. No way on this earth will a little key or a 1/4" groove hold that kind of force. It's all in the bolt.
After the keyway gets rewelded, I am installing a new OEM damper (again). I just purchased a right angle impact wrench because my real big one won't fit. The right angle wrench isn't made for heavy torque, but you can turn it as it impacts, unlike the guns, which I think will help. I am going to lock the flywheel somehow, or at least try. This will hopefully get me to the 200 ft. lbs. I need to keep it secure. This fix, if all goes as planned, should hold it, or at least hopefully until I find an engine installer.
If this works, or I even find a creative way to lock that crank, I will share it on the forum immediately. This is the first time I've been stumped when repairing an engine.