This was typical of what was being built by the "Big Three" in the 60's and 70's. No laser guided robotics making precision welds and measurements. Made no difference to the line worker if it was a high end car like Cobra Jet Mustang, Boss 351, or a station wagon. They had a production schedule to keep and sometimes just seconds to install their part on an endless line of vehicles that WERE going to be built and out the door that day!
I have friends who have restored Chrysler and GM products and have heard the same horror stories about missing welds, poor fitment of body panels, patch jobs to cover mistakes, etc. Got to remember, none of these cars were considered "Collector" cars then. They got the same attention from the line worker as a 4 door sedan or a pick-up truck. I feel these "Quirks and Things" we find on our cars give them their personality.
Wouldn't it be great to make a trip to that assembly plant lot and make a few selections! Don't want to be greedy, so maybe just 3 or 4 Mach 1's, a set of Sprint cars (Stang, Maverick, Pinto), couple of verts,......