Keep in mind a casting number is not a part number
A casting is pre-machined shape of metal
A part has been prepared post casting and is ready to install on the vehicle
In a few rare parts the two can be the same
But that would even preclude painting

Often for simple things the part number will be one off from the casting number
Sometimes when looking in parts books the casting number will be listed in the part description to help identify a part
I have seen instances where a casting is machined differently and can be found in 4 different part numbers

Engine heads were definitely machines different ways for different engines
But blocks I haven’t come across one but it could be possible
Maybe that is why the casting number can show up as multiple engines?