The engine number is stamped on the engine block, on a milled surface. It is not an actual plate.
Should be on the top face of the block at the front of the engine.
Expect it to be rusted over and hard to read.
Look out for milled surface on the cast iron block. Have a wirebush at hand.
Do not mix it up with the casting number, which is actually casted / embossed.
Good Luck Ralf