If you say that a spark plug fits the bottom of it, chances are it may be some kind of pencil coils. Pencil coils combine the ignition coil with the spark plug cover, therefore sitting on top of the spark plug and not needing a spark plug wire. However, i find it rare it came with your ace, as these types of coils are used mainly on modern sportbikes and touring options from bmw and the likes.
Also, I see a cable that may act as some sort of trigger signal from the CDI, but no charging cable? ( wire is too thin for this purpose?).