Yeah Danny, I agree that removing the t-stat is not the best test. IMO replace the T-stat regardless, just to be sure. If you were overheating real bad you'd have the typical symptoms. Ping, noise, smell, steam, bucking sometimes if it's real
bad, fire, nuclear meltdown, etc...you know.
Having the rad boiled and cleaned by a pro is never a bad idea either. The small cost is worth the effort, especially down there.
I hate old stock guages, especially GM. If it were mine and a resto I'd hide good guages to keep track of a $$$ motor. At least oil press and water temp. If not a resto then several quality guages in plain sight.
I too would get a good mechanical water temp guage to verify the actual temp. If anything for peace of mind.