Most of the nuts came out with minimal force, but the last one just spins in place. I tried rubber gloves, painter's tape, and duct tape to get a better grip. I'd rather not cut a slot in the domed nut if there's another good strategy.
The rest of the restoration underway:
The other side still has the bolt with the slotted head. I can turn it, but the nut and bolt just spin together.
Ahh I get ya now.
In that case I'd do what others have suggested and glue a socket to each side and use ratchets to undo.
Maybe you can clamp it down with something under the domed side so it won't turn when you unscrew the slotted side.