Manual mentions Dual Flash Lamp Board Assembly mentioned on 2-14 and 3-18.
Monitor lays down flat in cabinet, reflected up to mirror. Mirror has an overlay on it; left half blue, right half red, with explosion graphic on each side.
Flash lamp lights up lights up left when Player1 is shot; right when Player2 is shot.
Now to find a mirror to scan.
(click for full-size pic)
RELAX and just have fun. Remember, it's all about the games.