Not sure if I'm that familiar with the article you mention. Have seen dozens of article and books on what the authors considered original markings some better than others and often little or no reference is made as to plant, when during production or other details that might affect the use or non-use of a particular finding if one was made. Not really here to comment specifically on other peoples work but happy to share what I've seen and or documented.
Lets start with the first fact. The engines were all built at the same engine plant the majority of the markings would be the same no matter the car assembly plant. Of course there could be other, often only a couple, that may have been applied in house at the specific car assembly plant.
It appears that your asking specifically about the markings many apply to the drivers side cylinder head on 69-70 428CJ. These have likely been applied either because they found them or they just copied an article or someone else's car. I'm betting on #2 since this has been a very common copied marking since the 90's at least. Looking at the examples I have from 69 and 70 examples I found more that the always reproduced white "S" and sometimes a second marking. Not sure of the significance or meaning. Could be the line and have not cross referenced the few original marked engines to see if there is any correlation between the "S" and the type (CJ or SCJ) of engine. At least that might be the first step. Other markings I'm seeing/finding is a number not a letter.
As for other markings typically found on 69 & 70 CJ and SCJ
These would include markings found on items like the following that were attached to the engine when shipped to the car plant. Of course the markings would differ depending on the engine s specific details. Things like CJ verses SCJ, automatic verses 4 speed and so on.
- distributors
- carburetor
- pulleys
- driver side valve cover though as mentioned the other day in one of the threads there are a number of variations of this stamp used originally.
- exhaust manifolds
- paint markings at the rear of the block and internally
- markings applied to the front surfaces of the heads once installed and engine was paint as well as markings prior to painting the assembled engine
Things like air cleaner/shaker markings could differ between cars plant but can't be certain. Just trying to be careful.
Sorry I've not done a complete guide to the markings for this application as of yet
As for the specific question about the markings often found on the drivers
