Update: OK so I got a proper Torx to fit my 3/8" breaker bar, which I carefully turned and of course stripped out the torx head in the Freeze Plug on the first turn.
I invited a couple "professional" mechanics over and for $20 they brought the pressure pump w/ screw adapter for the cooling reservoir. We pumped it up and didn't see anything so I thought heating up the engine made sense. Then I put the valve cover back on, ran the engine for 20 minutes and we pumped up the pressure in the coolant system.
Guess what we saw? NOTHING! NOTTA! No leak of any kind. I even alternately pulled a plug wire to see if anything was leaking. after shutting down we pulled off the valve cover and I dripped soapy water around the Freeze Plugs, but I didn't see any leaks with the engine hot and the coolant system pressurized.
Maybe the slight turn before it stripped helped? I did slightly tighten the threaded plug before I tried to break it free the other direction. I felt and saw no movement.
The one mechanic thought that there might be a leak in the head???? If I understood what he was saying, he thought the valve head was designed as two pieces (a split head?) before the block and there may have been a leak from around a the spark plug? I didn't grasp any of that, as I believe the valve head bolts directly to the block (but I don't know this engine nor do I have a shop manual), but I found this online: http://www.enginediagrams.org/ford-z...al.html#more-4
and this image looks like it's a one piece head :
This same fellow is giving me a price for a timing belt job.
So where do I go from here with the leak that has disappeared? After much due diligence, including reading all the pros, cons, pluses, minuses, the patents, and numerous forum posts and mechanics testimonials and warnings, i have decided to add a product called Steel Seal to the coolant.
Steel Seal Claims and Information
I have to flush the coolant anyway as part of the planned car maintenance, so I will replace the thermostat/housing, and probably the water pump (with the timing belt job).
The vacuum leak in the PCV hose was a good find, so that gets replaced. (see my last post above - off-topic)
As always, constructive criticism, and input is very welcome! Thanks!
My Daughter is asking where her car is!