The bolts look too shiny to be originally installed. And I seem to recall there is a part number and Chrysler logo molded into the underside. For a time in the 1980s-90s, there was a shop in Los Angeles that would restore bent and cracked polyurethane bumpers, and if these are indeed 30+ years old, they may be original but restored.
There value has dropped some, since they started making reproduction ones. But there is still a demand for these, so you shouldn't have much trouble selling them, regardless.