I had to remove the adjuster on a threaded post from a #71. Here is how I did it. The bolt was rusted solid and would not move.
I had soaked it in penetrating oil for a while (almost a week) but it still didn’t want to move. I could heat it, but I’d still have to hold on the threads. So I cut a piece of aluminum flashing.
I folded the flashing and clamped it in the vice. The aluminum will not hurt the threads but will hold it tight.
This is a knurled nut so another piece of aluminum to protect it from the vice grips.
A few twist.
Oil it up and reassemble
Sorry for the upside down pictures. I’m not sure what that’s about.
-- Master hand plane hoarder. - http://timetestedtools.net