I am still trying to diagnose the issue with a lack of water running through the engine. I took the cover off the impeller (water pump) just to eliminate that as a cause. It looks fine.
So, based on on my gathered intel, I am now assuming that the problem is a blocked intake (thru-hull) under the boat.
That means that I need to go for a swim at some point soon. The temperature of the water is now 44 degrees. ?
Restoring this old sailboat is continuing my education on marine mechanics. Love it!