5 Answers

All modern automobile cooling system operate a temperatures ABOVE the boiling point, some as high as 235, Degrees F

The reason they can do so, is the systems are pressurized thus raising the boiling point of water within the cooling system.

The reason the run hotter is to increased efficiency in the combustion chamber and lower emissions

Then internal temperature in the heads around the vales is around 700/800 degrees F.

Then coolant moving within the head takes the latent heat away from the valve seats.

Several year ago Toyota had a sludging problem in several of the engines leading to premature engine failures.

The cause was a defect in their newly designed heads, intended to improve emissions, that cause the oil to "Coke" around the valve seats, resulting in oil sludge that destroyed hundreds of thousands of their engines, sold over several years, and millions of vehicles being recalled.

It cost Toyota billions world wide as well as a lot of lost customers

Has the radiator been checked for sodered veins or sludge choked ?     A consistant 210° is an indicator.   Remove the thermostat then run the engine.   Also, you can  test the thermostat in a pan of boiling water on the stove.  Cold its closed, in the pan it should open fully.       The other thing, do you know the history of the engine, seen it run.  If has been sitting a while anything could have crawled into it.  

That vintage engine runs approx. 190 degrees.

My vette runs at 220.. That's normal for LT1--

Are you using the radiator out of the 1960 vette or the Z28?  Was the radiator cleaned? how bout the thermostat?