I wonder if that old mag has a bad kill switch, or a shorted
kill wire. Mags are shut off by grounding the primary lead (the
connection between the coil and points) and if the switch is stuck or
the wire chafed against ground it will be dead.
Points gap in a mag is critical, since it controls the E-gap,
or the point in the magnet's rotation at which the points open.
Aircraft mags are set using various protractor tools or other means of
positioning the rotor for points opening; much more accurate than gap
setting and gives the hottest spark.
Bad capacitors are common, and I would expect a mag as old as
that to have cap problems. Without the capacitor it won't fire at all.
Lots of textbooks and mechanics teachers wil tell you that it only
prevents the points burning, but just try to run without it! It's
function is to absorb the coil surge as the points open to prevent
arcing; arcing both burns the points and prevents the sudden current
shutoff we need for rapid field collapse and hot spark.