That's a really interesting idea for that nice old cabinet. Fixing the old tube powered radio chassis is not too difficult if you like fixing tube equipment, but the proper parts can be hard to find for those old radios. I've seen one of those cabinets made into a guitar amplifier...
If you want an on/off switch, you can buy a combination volume potentiometer and switch. The switch is at the low end of the pot, you turn the volume knob up from zero and it turns on the power. A lot of old radios used a switch/ volume combination pot.
I really was torn between repairing the radio and replacing it, but the nerd in me won out. I do have another radio where the tubes look to be in fantastic condition and all it needs to new wiring; that'll be a different project for a different day.
That's a good idea for a power switch; I'll certainly need to look that up. Thanks for the pointer!