It is expensive but EVANS COOLANT is good for a problem situation, such as a modified engine with a shortened radiator where you just do not have enough radiator for the car and there is no good way to increase the size of the radiator.
I would not recomend it for a situation where you have a problem with the engine which causes overheating and you are using the higher boiling point of the Evans Coolant to get around it. In this case, I would suggest fixing the problem.
A GOOD MECHANICAL FAN is a big help on a flathead especially if you are running it in hot weather.
Just My Opinion,
Chris