These engines run cool with the 160 degree stock thermostat. Actually run better using a 180 degree thermostat.
The large surface area of the pan with the rough sand cast finish and the reinforcing ribs also working as cooling fins really help dissapate the heat. The sand cast finish has more surface area for heat transfer than a smooth sheet metal pan.
The friction modifiers in modern engine oil also reduces the heat from friction compared to the non additive mineral oil used in the 40's.
Classic cracked block will show signs of milky colored oil where the coolant has been forced into the oil. This condition can be checked easily with the dip stick. The pressure in the coolant chamber is greater than than the oil pasages after the engine is stopped. This when the contamination occurs.
A leaky head gasket will show signs of air bubbles in the top surface of the radiator
as evidenced when the cap is removed.
A leaky cylinder cover gasket will make the engine run hot because the air bubbles decrease the thermal film coefficient between the coolant and the radiator tube surface, resulting in a decrease in the heat transfer rate. The higher combustion gas pressure travels to the lower coolant chamber pressure through a passage way between the combustion chamber and coolant hole.
Normally, the block cracks between the top cylinder cover bolt hole and the exhaust valve seat because this is the region of maximum thermal gradient and resulting maximum thermal stress. The coolant then travels into the engine oil pan.
If the engine has over heated and conventional mineral engine oil is used the oil needs to changed because the lubrication properties of the oil has been greatly reduced from elevated temperature. Synthetic motor oil does not have this problem.