Keith -- Yes, I have a Shelby with the flat fiberglass outside panel. And the rivets have to fit into the small recess of the outside panel at the top. Thanks for the color feedback.
Jeff -- Thank you. That looks semi-gloss.
The first picture is similar to mine in that the Shelby side of the tail light wiring is hidden inside a vinyl tube or sheath.
As always, lots of other details in these pics.
It appears in the second pic (besides the stud and nut being painted and the use of tape rather than shield) that the yellow wire is trapped under the tail light bracket. The black and red wire looks kinked too.
In order to "give back" to this thread, here is a picture I took many, many years ago when my friend owned a GT350 and he had to replace one of his brackets.
He got sent the wrong one, but for some reason I took a picture of both.
So here are the deep and the shallow brackets together.
The paint is too glossy, so ignore that.