[55wagoncrazy]

Dimple was put there for the mounting of the front stabilizer bar. Early ones even had a hole in it. I believe this was the plan, and the
maker of the control arm made them that way. By the time the cars were getting made there was a change to the way the mounting
was made, by then the tooling was done, and there was no reason to remove it.

 

[55wagoncrazy]

The design of the lower ball joint was very good. However mechanics were taught to lift the suspension with a jack to check for ball joint
play. The lowers would come out of their seat when this was done. The ball seated properly when the coil spring was in place.
It was the way they were designed. So stupid mechanics would replace good GM ones with inferior ones and charge for it.

This is about 98% of the reason lower ball joints are replaced even on very low mileage 55-57 cars

Not 100% of the lower control arms had the dimple. There were many suppliers for the frames and parts used to build them.