Nice! WTF are you cutting that nut with? Some great ideas there and an elegant solution.This is the easiest way to do it. Just use the nut/ washer from output jack. You’ll need a couple extra washers to space the switch on back side.
Cut the threads of the nut off to make a washer out of the nut. Use the spacers between switch and chassis. Install nut/washer on front side and use the nut that came with the switch to secure it.
To hide the switch inside the jack and recessed like in the picture of my 69’ I posted requires cutting the entire jack and using epoxy to secure the switch.