Quick update, mainly for anyone searching threads with the same issue in the future... I finally got around to getting the old torsion key off. Had to cut it, which was a pain. It took a combination of drilling holes and angle grinding, along with loading some tension on it using the torsion key tool. It eventually snapped right off. I then had to grind off the 6 bolts that hold the torsion crossmember (3 on each side) so I could get the new one on. I made sure to install the new key one rotation further clockwise than the one I removed.
It now looks too high into the crossmember, as it's already above the keyway without any tension on it. I'm going to see how it sits with everything buttoned up and some weight on the front. My guess is the torsion bar itself is worn out or possibly not the correct one for the truck.
So I may be stuck with either an underloaded torsion bar with the current clocking, or reclocking it to the original position and overloading the torsion bar. Since this is a farm/plow truck, I'm not too worried, but if I were doing this correctly I would probably replace the entire torsion bar.