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Operating range of 160º to 210º F."
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On a carburetor-equipped engine, often a 180º thermostat is used, although a little hotter thermostat rating (190º-195º) may make the motor more responsive and add a little fuel mileage. It may also help to burn off some of the by-products of combustion, such as moisture and acids which form and get into the oil."
The above can be found in this very informative article related to
Bulletproof Cooling SystemI have an "off topic" 5.0 HO motor in my '27 roadster pickup hot rod that runs about 195-200 F. consistently. I thought that was too hot, did some research & found the above article.
The article is consistent with other technical articles I have read that conclude that keeping the engine cool (in the lower part of the 160 to 210 range) is not a good thing. So the temperature you are describing at the upper end of the 160 to 210 range should be good for your 250 cu in. engine.
Also, be careful about running less than a 50/50 mix of antifreeze. When the concentration of antifreeze gets to low severe corrosion can occur. This is especially important if there are any aluminum components in contact with the coolant.
Hope this helps.
John
