Aftermarket is a possibility. With that being said, why wouldn't these make appearances on other vehicles? Yes, my mind is pointed toward a factory part for 1947. The front bumper for a 47-48 GMC is different than 49 and up. Common knowledge. But not so common is that the 47 bumper has 4 extra bolts in it. The parts books make no mention of this but there are enough examples out there to make the case. The hood hinges are another area where they are known to be different but no part number difference. Maybe because the part number was superseded and both parts are interchangeable so only the new number is used? Not sure why. I just found 3 examples of this part, all 3 are on 47 GMC trucks. I just want to see 1 or 2 on a different vehicle to convince me. Meantime, I will be looking at some old JC Whitney catalogs.
