I think you have 2 different issues.
Since you worked on EM games I assume you know how to solder? Your going to find that these old Bally SS games many of these problems are cold solder connections to the connector pins on the boards. Best place to start is to reflow/resolder all the connector pins on the boards.
Lets start with the flippers as that is the easier to troubleshoot. Since the other coils on the playfield work The flippers are probably tied to bad connections on the solenoid driver board. That's the board to the top right of the game. Check the connections on J1-3. and the relay it'self. Reflow those and your flipper relay should kick in and you'll have flippers.
As for the Displays,
Reflowing the connections might help. All of these connections trace back to j4 and j1 on the MPU so as a last resort you should check those connections.
Finally post some photos of the game and boards. If there is a battery still mounted to the MPU, remove it. Those leak over time and damage the board.
Good luck, awaiting your results...