A multiplayer game doesn't have a ball count unit, they 90% of the time have player units, and 4-player games have player units 100% of the time, just like the games mentioned above. (Honey and OXO) They will not work. For the advance unit, more likely it will work from one of those games. (Read below though!)

That little thing is the match/0-9 unit, not a bonus/advance unit.

You need a SINGLE PLAYER ball count unit, and also one that does step up and step down instead of just step down and full reset due to the nature of this game when in add-a-ball setting. (This game can be set for replay play, add-a-ball play, or novelty play - a feature unique to Williams EMs)

Huh, really? Most of my experience is inside of my Gottlieb games (like a ton, oddly enough), but I've never noticed "double units" on my multiplayer Williams games either. It is entirely possible I missed them as I haven't been inside of them nearly as much (again, oddly, but I'm not complaining!) but I don't understand why they would use both.

Are you sure? Interesting.