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.
The screw doesn’t have enough exposed thread to get a good grip with the vice grips. Tried out needle nose grips and it was just spinning on the threads still. The screw isn’t replaceable and I wouldn’t if I wanted to, but the nut is replaceable so I might try splitting it. I would be very worried about damaging that screw though as it would mean a new steering gearbox if I did.
Pinching the nut off could damage the threads so don’t do it. It’s not a big chance but there is a chance. If you can get a file in there and get some movement you can spend hours cutting it that way. It’s the long way but the safe way.
If you have a good file it might only take a few minutes that nut looks like soft metal. But no on the nut splitter. If it was .cheap suspension part yeah but the pinching could crush your threads on the screw.