Very odd engine stamp

[SS427]

I just looked at a well known COPO Camaro with a very odd stamp and was wondering if anyone else has ever seen this before. The car is very real, well known and with loads of paperwork and all original drivetrain. The owner states that the engine was only rebuilt once and was done by him and no one else has laid hands on the car other than himself. The photos aren't the best but they were as good as I could get. The engine code stamp is T0822MN and stamped directly over that with the same size font was "EECCSSMM". The owner has NO idea why it was stamped like that and insists it would have been done before he bought it (original owner) and insists it was not done by an engine re-builder as he owns his own shop. He also stated that when he rebuilt the engine MANY years ago it had never previously been apart and still had it's metal head gaskets. The VIN is also stamped on the engine and is an exact match of the VIN on the trans. I have ZERO doubts about the car or it's drivetrain but wanted to see if there were any other examples like this out there.