Looking at the engine tags I have pictures of so far it appears that only one plant used a plant identification code on the aluminum tag so that sort of kills the focus of this thread I would think unless others see an angle I don't
Below are exampled of 69 on the left and 70 on the right for some of the engines. Don't have enough to cover every combination and no 6 cylinder examples at the time
PS - Added a note and link to my post above related to the sticker and the use of the "D" in the coding