Here you can see I have switched the tool locations. There is now enough clearance below the nut to clamp on the Vice-grip pliers, to continue and hold the piston from rotating.

Notice there is a little damage at the end of the shaft from the previous Vice-grip contact, but the nut still comes off with no problem. It doesn't really matter if you mess up the threads BELOW the nut since we are not going to reinstall the old shock.

Continue with the wrench. Once the nut is off, you can remove the old bushing and washer.

Now we move to the bottom of the shock.

On to the next step.