Mine is a Metucheon car. The date code on the door data plate is 15 M.
The heads have a 5L5 date code. The intake has a 5H27 date code and the engine assembly stamp is 5M21d. I lost my picture of the engine block casting date. It it too hot right now to get under there and take the starter off.
The transmission case has an L-8 date code. The casting code on the transmission case is C5AR-7006-D W-2. The tailshaft has C4ZR-7A048-A and date J22.
The diff cover has what looks like 5M10 date code.
So it is established that this happened more often at Metucheon? Do you know if they marked replacement engine blocks any different than the original blocks anywhere?