Tim,
I have a Branda CS kit, it came with a sketch supposedly from Shelby noting the pedetal mount of the Lucas lights to the grille inserts (lower "L" pices) drilled thru the lower grille molding and the stoneguard.
That looks like a standard 68 GT fog bracket. Was that used on the Shelby's, or a CS style pedestal?
Do you have a pic of the actual mount of the lamp to the grille from the front? The CS kit has a tubular threaded sleeve-nut to fit below the fog. I have seen some references to Shelby's with a larger square chrome base piece (I have a few of these as well, very different than the Branda CS kit).
Most of the pics I've seen of 68 Shelbys are as below, which appers to use the pedestal mount, not fog grill bars??? Or is there a difference from GT500 to GT500KR? Hard to tell how its actually mounted from your pic.