There are two numbers on the engines originally fitted by the Ford, the VIN number end sequence is on the turbo side of the engine block as per your pic, and the actual cosworth engine build number is on the front of the block by the thermostat. These numbers will always be different.

The front cosworth engine number on an escos starts with YBP for big turbo and YBT for small turbo I believe ( 3drs and 2wd saff are YBB and 4x4 were YBG and YBJ depending on whether green top or not and RS500 engines start with YBD)

If the side numbers are missing but the front is present then its had a factory replacement engine and if both numbers are missing then its had a new block.