Like Walt says the numbers on the dist pad indicate the actual assembly date. It can be as long as 30 to 90 days later than the casting date.
It all depended on foundry and engine plant production schedules.
The JC or other letters that follow the stamping define what vehicle and powertrain options that engine ended up with. Powerglide, Manual trans, Passenger car, 1/2 or 3/4 ton pick up, etc, etc.
The CON 4 cast in the block identifies what conveyor the block travelled on during production.
Totally meaningless to anyone except if there were warranty problems. The factory could then narrow down the area during production where the problem might have occured.
A good source for interpreting suffix codes is a Service Trades Edition of Motors Manual that included the year of that engine / vehicle. These pop up a lot at swap meets from people selling shop manuals and so on.
