My 59 235 runs a 180° thermostat and runs at or really close to 180° when hot, regardless of the outside temperature, so my recommendation is 180°.

By the way, I run a 4 lb. cap on the radiator.

Phil
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1952 Chevrolet 3100, Three on the Tree, 4:11 torque tube
Updated to: ‘59 235 w/hydraulic lifters, 12v w/alternator, HEI, PCV and Power front Disc Brakes
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