I never got around to drilling my fender and left the plate "floating." (Call me chicken too.) The licence plate frames we used to mount flush matched the fender pretty well. You can see a slight gap at the left and right edges. Careful not to tighten the screws too tight. Seems that could damage either the fender or frame. Cover the back of the licence plate itself with something like duct tape to you don't have metal to metal on the paint.
I have a sheet of rubberized cork gasket material I intent to use as backing material. So its back to the drawing board. The frame seemed to have about a 1/8" gap on both sides within approx 2" of the edges.
Also drilling through the thick steel support ate a couple drill bits (tuff stuff)
Biggest issue is how to get it perfectly level with all those radius edges?
From the side you can see how it stands off the fender. Also could not find the right body plug for the 9/16" original hole? Tried Ace Hardware and Napa so far?