The late 1955-63 (not 235 vs. 216) water pump has far more capacity than the early pump. Its rated output is 14.5 GPM (gallons per minute) per 1,000 pump RPM, 72% higher than the early pump at 8.4 GPM. In use, the water delivery rates are more similar because the early pump turns faster due to its pulley sizes.
Are you sure your spark lead is correct? Running at near TDC timing will be hot.
Does the fan have a shroud?