The person I owe the biggest THANK YOU to is my friend, fellow Pantera owner and expert problem-solver Bohdan G. He suggested my carb may have leaned out and wisely asked when I had last adjusted it. The answer did not impress him and he immediately came over and spent the evening helping (and teaching) me to adjust the carb. As an added measure of safety, I decided to move to a slightly cooler spark plug than I had been running (NGK UR5 from a UR4). As we were finishing up and doing some running tests, one of my fan relays started acting up causing the fans to stop working and we called it an evening.
Tonight another friend, neighbor and car-guy (who is less intimidated by volts than I am) came over to help trouble-shoot and locate a loose connection at the relay. Once all was tightened up, we went for a 45 minute drive (low and high-speed areas) and SUCCESS! The car ran like it did when I first got it. Strong and no pinging at all, even at the hottest temp. It never went over an indicated 195° on the gauge — WITHOUT using the second fan (my '71 has one switched fan, one thermostatically-controlled one). When we returned, I left both fans on and let the car sit idling for 30 minutes in my driveway and it stayed UNDER 195°.
I also took my new infrared temp sensor and found that the hottest part of my heads was 200°. My rad at the hot-in area read 193° when my gauge read just under 195° which suggests that the gauge is pretty close to accurate in my case (like Garth's).
Anyway, a HUGE thanks to everyone for their input, and ESPECIALLY Bohdan
for SOLVING my conundrum.
Mark