Given that the crowbar overvoltage protection requires a panel-mounted breaker, make it a pull breaker and when you want to shut off the alternator, simply pull the breaker. That way, you only need a single switch for the system master switch and can get rid of the split-rocker master switch.

Contemporary key-type magneto switches are fat, ugly, expensive and heavy, and they provide only a modicum of protection against airplane theft.

Instead, use two DPDT switches to control each magneto, with one spring-loaded to center. The p-leads are grounded with the switches in the lower, OFF position. The center position of each switch un-grounds a mag allowing the engine to run. The spring-loaded upper position of the left switch controls the starter solenoid. The starting circuit is completed through the lower, magneto-off contacts on the right magneto. This interlocking prevents inadvertent engine cranking with the right mag energized.

A diagram describing this can be seen in Figure 13.