A few months ago I had same stuck knob on my 66 redeye. I used a strap wrench and some powdered rosin to get mine loose. You can buy a small inexpensive strap wrench at auto parts or tools store. These will not damage the metal. Powdered rosin is a great gripping agent, you sprinkle it on the strap and it helps it grip the knob. You should be able to buy some at a music store. Its used on violin bows I think. I have a big jar of it I got from a gunsmith supply house years ago. Good luck.