The caffeine has worn off.
I am 99% sure I have just a hogged out holes with no threads. Keps nuts would be one solution but I am sure I have enough hardware in inventory. I'll sit tight until the relocation bracket and LED are available.
This will confuse a bunch of folks so I'll try and clarify it again. The lights are all grounded via connection to the tub sheet metal and the screw threads in the threaded holes. There is no need to ground the tail light housing. All we need to do is get the Keps nut to bite into the sheet metal on the inside of the tub and my grounding method will work perfectly.
The other reason that needs to be clarified is I supply some glue strips to lay down to mash the little wires into for routing, then another goes on top of the wires to make them behave. Most will cover the hole in the housing used for the ground screw and they just need to push the screw through the glue, it doesn't need to be cleaned out of the countersink for the ring terminal to make contact with the housing because the housing is not grounded, the screw is. If the screw is in contact with the sheet metal of the tub, it is grounded.