Another followup, to anyone interested.
New radiator works great, but that pesky temp needle still reads above what I think it should.

So back to my mechanic, to get a new thermostat. We were going to do this before, but did the fan clutch instead.

He puts his little socket wrench on the thermostat housing bolts, and announces that they will surely break off before they come undone.

Well, we then made it so the electric fan was on all the time, hoping to keep it cooler. It just did not work, the car ran fine, not overheating, but still warmer that it did the past two or three years.

I took it home, and applied P. B. Blaster to the bolts, and tapped them gently with a small hammer a few times, and more P.B. Blaster.

The next day, I got my wrench on the bolts, and got them started out. The "tink" as the bolts started out was like music to my ears!

Back to the mechanic, who seemed surprised that I was able to get the bolts loose.

Anyway, the thermostat that came out of it was a German one, with no markings as to it's temp range. The rubber grommet/gasket was silacone sealant...but you know, it never leaked.

Anyway, my guy uses the truck thermostats, because they are available with a lower heat for down here in Florida. New grommet too. The M.B. thermostat also has a hole in it that facilitates the air to purge from the system, the one that came out does not.

She now runs cool as a cucumber, right at or below that line on the gauge, with the A/C on too.

The engine must be much happier....I know I am.