Mystery panels found om my 63 behind grill and fenders....ID help needed

[1963c-10]

Noticed these when I go the truck originally and have never seen another set. Didn't really think much of them, but with the engine and brake swap going on, the front ends coming off this weekend...they peaked my interest again and just wanted to see if anyone else may have any info on them. I have looked in all the factory literature I have and haven't seen anything from GM on them....even the silver book and custom accessories manuals had nothing. Maybe dealer installed or aftermarket? The quality of the panels are nice, doesn't look like some spare sheet metal and tin snips. The edges are finished nicely and they fit very well. There is also covers over the back of the grill where the headlights are. These panels are on both sides.

They do serve a good purpose....keeps mud from getting in all those hard to reach places that cause rust issues, so I plan to clean them up and reinstall. The 63 also had factory mud flap at some point. There were some pieces and the mounting bars left that I've since removed.

Anyways...just wondering if anyone else has encountered these mystery panels or had any info on them. Truck was shipped to PA originally from Baltimore plant if it helps any. No ID or part numbers visible and they are bolted in. There is glenwood green overspray which is the correct original color, truck has been resprayed once since factory, but cannot tell which paint is on them, but they have been there a long time.

1st pic is behind the grill driver side and the other two are the driver side wells towards the cab. You can see in the pic of the rear panels about 3/4 down the panel where the light brown strip is, where the mud flaps were mounted.