There is a small plug on the left side of the engine as it sits in the car, (right side in the plane) at the lower part of the center iron.  It is adjacent to the grounding plate for the ignition.  This plug will drain coolant from the engine.

Has anyone tried installing a drain cock similar to what you would see in the bottom of a radiator in this location?  Do you know what the thread sizes are and what would be necessary to install a drain cock?

Bill B