The distributor that was used with the polarity reversing switch used a set of points that was insulated from the housing. If the reversing switch is not used, it's necessary to ground the non-moving point to the housing to complete the primary ignition circuit when the points close. That switch was only used for a short time, without a sufficient increase in the life of the points to justify the complexity of the circuit.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!