Have a 65 Belvedere that is undercoated inside the doors and there are 2 metal plugs on the door backs where it was sprayed in. Anyone know if this was this a factory deal or an aftermarket dealer applied or a Ziebart, Rusty Jones kind of thing. The holes under the plugs are kind of crude which made me wonder. Silver plugs I'm talking about in the picture are up near the top even with the outside door lock and other is lower, even with the rubber bumper.