Is the Mooney clock opening 2.25 inches?

Maybe someone can save me a trip to the airport to measure.

Specifically, looking to mount a Davtron 800 clock, will it fit?

While I'm at it, is there a convenient way to wire the clock for continuous
power when the master is off, or do I need the "B" model clock with the built-in
alkaline battery clip? I know the cabin overhead light is powered with the
master off.

M20J, in case it matters.

Thanks.

Dave