This problem could be an issue with many different vehicles not just A-body's.
I had let my father borrow my '68 GS (a stupid decision in itself),he calls me two weeks later and said "the car wouldn't start AND the frontend needs alighned because it's popping".
Upon investigation I discovered that the front shims that were most likely installed at the factory, had only been pushed half way down on the bolt and after 50K miles they fell out! This left the bolt very loose and it kept working the nut off. The back bolt eventually sheared off at the head. Fortunately the loose nut had about half a turn left or the upper control arm would have come completely off. As it was the wires were ripped off of the starter when the bolt sheared and dad thankfully was unable to drive any further!
Moral of the story? Check your control arm nuts and don't let dad borrow your cars!!!