My guess would be Box 3 is a bowling toy of some sort, probably drop target/lowering bank style. Very central to the theme and a nice straight shot fits for the bowling. Maybe it feeds that wireform coming out of the center back? It also seems like the ramp shot on the upper playfield must go up into area 2, since otherwise I don't see how the stacking works there. There have been simpler / more compact versions of that plunger lane going into the ramp design, so maybe that will get some revision.