Grounds are easy. In the back box in the middle on the bottom you will see a 1/4" braid that runs down into the lower cabinet. That's ground.

Eight Ball was the first pin I restored electronically several years ago. Rebuilt power supply, all board pins and connectors were replaced and new chip sockets, except for the light driver board...don't do that one unless there are obvious problems. If you do this work to the old Bally MPU's they are pretty much bullet proof. That game has never failed since.