Well lets give this a try.
In Tranny 4 I don't see any shadows or marks. Maybe they didn't show up because of lighting (too bright or poor angle to see the) but as the article metions above the shifter studs we see what was likely a assembler number done in a stylish font from the period
In your passenger side pictures. I looked at other examples I have and some other top loaders being built before and after the HEH-BX. Typically the same workers that did the -BX and for the same purposes so their might be similarits.
I start out colorizing the different shapes, letters or numbers in contrasting colors to try and make out what they might be. In other examples I'll do every stroke or line in a different color. Not unusual to find them over lapping to make the process even more fun

Tried to try and guess what is going on around the filler hole on that side since it appears there is staining in a somewhat large area there with no clear indication as to direction or easy to determine shape.
The orange stripe or poorly applied check mark is found on a lot of examples
The large X or V is often found
A far number often had a large R on that side though not getting that from your picture
Red arrow at the bottom of the picture is pointing to possibly a few more stains from other letters or numbers that were applied to the bottom of the main case.
Yours

Highlighted

Here is another similar top loader with a couple of similar markings

Other places to look
- At the forward flange of the drivers side of the main case as shown in the article.
- Tail shaft housing. Above and or below the speedo attachment hole
- On the bottom of the tail shaft housing behind the rubber mount in the oval depression area
Some examples

Hope this helps