My pump did have the junction box mounted there, but there was no hole on the center. The square metal plate on my pump is aluminum. The four bonnet mounting bolts are carriage bolts, probably not original, but they work.
It seems like rain water could enter the large center hole and go directly into the cylinder. There has be be some type of seal between the jar lid and the square plate.
There must be someone that has photos of a 600 series Tokheim visible above the jar lid.