That layout can be seen on a lot of Gottlieb EMs from the 70s, where the ball-in-play lights are part of the backglass artwork.

That layout was done just for aesthetics, so that the numbers would evenly span the artwork space when the game was set on 3-ball play. This was at a time when 5-ball play was the norm, but due to the economic recession, some operators were starting to switch over to 3-ball play to keep the games profitable.

I was always proud of the fact that the operator I worked for was totally against ever putting a game on 3-ball play, and so we never did. This isn't such a big deal on a modern game, but on those 70s EMs I think a 3-ball game is very short.

- TimMe