This mystery kept nagging me so I decided to look through a lot of my saved engine VIN stamp pictures. My goal was to see if I could find any with a similar set of indentations, like yours, along the angled portion at the top of the VIN pad. I found a T/A Challenger 340 engine VIN pad showing these indentations although they are rather faint in comparison to yours.
It is my belief that the factory's Gang Stamp Holder may be responsible for these indentations when they "strike" the die with a dead-blow hammer. I have included pictures of gang stamp holders used for non-Mopar engines at the Brand-X Tonawanda engine plant. I believe that Chrysler engine assembly plants used a similar device to stamp our engine blocks. The T/A stamp below looks like the stamp holder skimmed the angled portion leaving the faint marks.
If the holder is not held in the right place and perpendicular to the surface, it would result in these indentations. This would have been the first strike on your VIN pad and would require a second strike to get the VIN properly stamped. I believe this would also create a "divot" in the lower part of the pad as the corner of one or more individual dies unintentionally struck it. This may explain some of the additional marks seen at the base of your numerals.
Your VIN stamping is the most pronounced I have seen but you can see the same VIN in the indentations above along the angled surface.
Not saying it explains the odd "2" or "7" but you definitely have a mystery here.
EDIT: Barry Washington of the Hamtramck Historical site and of T/A fame said in another forum thread that the stamp holders had roller dies versus individual stamps.
That would speed up the process but the indentations would still be possible as the edge of each die in the roller would create the squared portions and/or divots.
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And a modern version still available.
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