I did a search and didn't find anything on the subject:

I have a "plain Jane" '58 with painted front and rear bumpers. The rear license plate is not displayed very well- it is behind the rear bumper and (I think) bolts to the structure under the tailgate. I don't think this is stock. What is the stock mount for license plates? Do they bolt directly to the bumper? Can anyone direct me to a picture of what it is supposed to look like? Might as well throw in advice for the front while you're at it.

Bill