Model N serial number location

Where is the serial number on a model N stamped? I looked at a car the other day and we looked all over the engine and couldn't find any stamped numbers. could this be a replacement block?:confused:

It's stamped on the aluminum crankcase, on the carb side of the engine, above the access cover toward the rear of the engine (right by the cylinder/crankcase joint). Early engines had no raised boss where the number was stamped, but later engines had a raised boss.