After the fast response from my fellow HAMBers on my last unknown piece of metal, I came acrossed 2 more I have no clue what they fit, the tags say 50s MOPAR, and they came in a package deal with the 51/52 pontiac lower grille bars that you guys previously identified for me. So heres some pics of a rocker panel and another panel. rocker part #1577413: unknown panel: Thanks in advance!
I can narrow it down that their not 52 dodge, as I just reproduced a set for my junk. See the pattern in the pic, but picture a flange turning down@ solid back line. Yours need the inside piece, although a simple 1 bend flat piece. The outer edge offset where the door resides is only a 1/4". Yours look a lot deeper.
My guess on the unknown panel is some kind of gravel guard, or however those are called, that goes under the lower valance to protect the front crossmember/suspension/radiator from road debries.
I put a '50 DeSoto together a year or so ago and that unknown panel really looks like the plate that goes between the grille and top of the radiator from that car. Would have to doublecheck but it's very familiar.
the 15****x part number would be for a 54-55 era mopar, if it's a mopar part. They ***igned their part numbers sequentially, so you can figure out what year something is by the part number. You might see if the shape of the rocker matches that on pictures of 1955 plymouths or dodges.
Now that you say it it sure looks like that. too small for what i was thinkin, but didnt notice the boot marks till now.