F523J
F = Flint, MI plant
5 = May
23 = 23rd
J = 3100-3200-3800 regular production 235 truck engine with mechanical lifters (originally used in a manual transmission truck)
F218 - block date casting code
F = June
21 = 21st
8 = 1958
Most likely the valve cover is attached with 4 machine screws on the side.
Most likely, the water pump body is completely below the head.
Here are locations of other casting codes 
