May have found the original location where the engine ID stickers were applied but since I only have documentation of one example so far I'll not post a picture of it since it should be confirmed with additional examples IMHO and if I post a picture some viewers may just see and replicate at this point.
The location is similar as used on some other engine sizes the same year and prior years and would be hidden from view (one of the reasons we may not have seen them over the years) and lead to them not lasting over the years also.
Will continue to search for additional examples now that I've got a clue. Guess I should at least share the general location so others can search also
![Smiley :)](https://www.concoursmustang.com/forum/Smileys/default/smiley.gif)
Look to the front surface of the drivers side head. Location sort of makes sense and would be a logical alternative to the worker in charge of placing those stickers.
The location would be hidden on most cars because of the AC compressor and mount - Good hunting