I'm wondering if the connectors are on the right way round with the l/h display - they probably only go on one way, but it looks a bit clumsy like that. The grey ribbon cable seems to be right, the red stripe is pin 1, and I think I see '1' screened onto the pcb. The glass display envelope often shows tiny metallic speckles around the segments when it's failed.
It's blooming awkward that the two display boards aren't interchangeable; on the oft-reviled '6803' system they were, and the games had a facility to operate with only one display, allowing a maximum of two players per game. As far as I can tell, with this set-up, the r/h display is the more important, since it receives the 'bcd' data from the cpu board (on that extra connector). This is then passed across to the left display using the ribbon cable.
The inter-connection info in the manual for this game says that the two display boards pin-outs are the same, but with the r/h having the extra stuff. I take it that means the r/h display could be placed on the left, but all that you might see is a faint glow from part of the envelope, if it's okay.