Check out Dave Wise's book on E-body Fasteners. He has pictures of the type of fastener that SHOULD have been used for that application. My AAR had the fastener with the machine thread that matched the machine thread in the square valance nut on the bracket. I've seen some original AAR's and other E-bodies with the chrome sheet metal screw "forced" into the machine screw nut but really don't think Chrysler would have installed a square machine nut in the bracket only to use a sheet metal screw. It is possible that they came both ways. Probably what happened is the line worker had easier access to particular fastener at the time the car came by. If he had easier access to a chrome sheet metal screw (and he was a little bit lazy) the he just "zipped" that in rather than look for the correct machine screw fastener. Like it was said earlier, the quality control wasn't the best back then and this was more or less on the underside of the car, so who cared, they didn't know that we would be analysing their work 47 years later.