Yes, capacitors used in parallel with points in ignition circuits, whether magneto or Kettering (battery/points/coil/capacitor), have a special kind of construction. They have to have a high voltage rating, be physically robust because of vibration, and be able to stand thermal cycling in the presence of moisture. The high voltage rating is because the voltage "kicks back" across the points gap while the circuit is firing. The capacitor needs a 600 Volt rating. Of course it also needs the correct capacity (measured in microFarads), or one or other of the points will erode quite quickly.
