Robert,
Yes the magneto is missing the contact breaker assembly, and the protective cap that covers it. The contact breaker assembly plugs into the female taper dead center of image ef_1_b.jpg (note how un-weathered that area is.) The breaker is operated by the internal cam ring, still in situ. For the magneto to work the electro magnetic field needs to reverse and collapse. Normally this is done by the contact breaker separating abruptly and at the optimum time to maximize the spark intensity. But the same thing will eventually happen on its own by rotating the armature. Were the contact breaker fitted and functioning you would have got a much stronger shock.
The magneto has shielded outputs to prevent radio interference, so without looking up that model number I am thinking military. Perhaps fitted to a Douglas generator set, ex- war department. The motorcycles from 1946-1955 used a Lucas MagDyno to provide lighting current in addition to sparks. Not sure if the commercial engines after the war use shielded ignition, but doubt it as it added to the cost.
-Doug
