71 Dart Fender extension bolt holes stripped

In the process of putting my 71 Dart back together after paint.. got the rear quarter extensions and bumper on .. went to put the front fender extensions on .. and the holes (I think there are 4 of them per side) are stripped out.. the holes look like they're some kind of plastic/resin/fiberglass or something.. and the bolts that are there to attach them won't 'bite' because the holes are stripped out. Any suggestions?