For reference this is a 5/8 lock nut with an Allen screw inside. It was so seized up, we let it soak for 3 days with antiseize, tried head and freeze method, and nothing helped. Still ended up with a stripped screw. I’m at a loss at this point and not sure I feel comfortable grinding a notch into it.
You did loosen the nut first, didn’t you? You are adjusting the steering box?
Yes we had loosened it about 1.5 full turns and then held it in place with a 5/8 wrench wedged into the radiator support and the screw is seized into the nut itself and nothing was getting it loose