You should see a good spark at the points when the gear is turned by hand and you can put a plug in one of the plug wires and ground the plug's threads to the mag body and turn the mags gear to check for the spark at the plug.
Joe Hunt Magneto's, Magsarus, are a couple of the rebuilders.
While sending them to a rebuilder isn't a bad idea, mags tend to be pretty bullet proof. Pull the cap and hold the wire that goes up into the cap about 3/4" away from some grounded metal. Turn the distributor gear by hand and see if it arcs.... If it does, stick it in an engine and see how it does. Do not touch either the ground lug on the side or the wire out of the top, it will shock the chit out of you. Done that!!..
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