Retard magneto

I have a Slick mag with retard breaker that I took off the engine to put in an Electroair on one side. Now my regular magneto has about 500 hr and due for overhaul. The question is, can I replace it with the lightly used retard mag? I have no need for the retard function as I start with the electroair.

Seems like you could as long as they both have the same shaft rotation direction, clockwise (R on the data plate) or counterclockwise (L on the data plate) which should be the case for a 540.

I retained the retard mag (on the left) and replaced the 25* fixed right mag with a LightSpeed Plasma3. Like you I only start on the electronic ignition. So guess that answers your question, yes it can be done. Now at 600 hours and with one 500 Hour service done on the retard mag I’ve still got the new “fixed” mag on hand and will use it if/when I have to....... Of course then, like you are already doing, it’s imperative that the fixed timing mag is not used for starting.