NEW PROBLEM! Getting everything ready for my EVANS waterless antifreeze meant getting as much of the old coolant out of my system as I could. I had flushed the radiator and the new motor was shipped to me dry by MRL. That left the heater core to be flushed.
I cranked the pressure down on my compressor to 20 pounds and blew through one of the heater hoses while I caught residual coolant from the other. As I left it blow for a few minutes, I went inside the car to listen. I could hear an air leak from the heater housing. So, it looks like I need a new heater core.
If I can't get one soon, I'll plug the hoses until one arrives. - I'm off to the parts store again.