I am thinking that since the air cleaners are not centered on the carbs and cantilevered in the cut away they may vibrate loose or stress the air cleaner itself with an offset fastener in the center of the carb. Two fasteners spred across the air cleaner would alleviate this condition.
Just trying to get rid of theses pictures I got on my PC for years now...lol... ...almost done, just a few thousand left..