I think you're right-on about that bracket Mike. Here's photos from Coplite's website showing their "SWING DOWN HOT SHOE" model lamp:
Looks identical to me.
I didn't find a single hole drilled anywhere in that car so if it saw LE duty, they must have been using only mobile comm equipment with it. I directed the owner to go seek information on his car from the county's fleet department. I hope he does and gets back to me.