Why Mix Ignitions?
The life-cycle cost of mags exceeds the initial higher cost of an EI: inspections, parts, expensive plugs and harness. Why are you retaining one mag? If it's fear that EI's are failure prone, why are you installing even one? Mags fail, too.
Then, you have increased your parts count, inventory needs, and skill set to service two ignitions types. Since the mag doesn't contribute much to the engine's operation with the EI lighting the fire sooner and hotter, why keep it?
John Siebold