Is there any reason there would be no casting numbers on the block?
Casting numbers are part of the block mold - all blocks should have casting codes/numbers, unless someone ground the casting codes/numbers off.
The engine serial number is pressed into the block when the engine is assembled for a specific vehicle.
A factory replacement Chevrolet engine might not have anything in the engine serial number location. The installer of a replacement engine might press/stamp a serial number in a block. However, there might be no engine serial number if the installer did not put one on a factory replacement engine.
Another reason there might not be an engine serial number is the engine might be a used replacement engine from another vehicle. The installer might then grind off the original engine serial number and then leave it blank (this was the case with the engine in my Suburban). Or, the installer might stamp into the block the ID/serial-number from the original engine that had been installed in the vehicle (in states/locations that used the engine serial number for titling/registration purposes).
GMC replacement engines usually came from the factory with the cubic inch displacement pressed into the block. This was a normal part of the engine ID/serial-number. The installer might then add the rest of the serial number (or, the installer might add nothing - this was the case in my COE).
