2 of the Bally games I have in my possession have the "lift-out mounting board" I think they did away with it when they introduced the newer style coin door
https://www.ipdb.org/files/201/Bally_1966_Bazaar_New_Lift_Out_Mounting_Board_Instructions.pdf
I am not familiar with the add-a-ball relay or any documentation on how to make it work.