Yes it must be the 340 four barrel badges on the hood the restorer added 6 way seat , rear sway bar & electric windows from a donor SE but they were later it has a Galens report but the 10 was not mentioned.
I've seen several tags with similar stamps and some with holes punched right through.
in fact go on google images and look up "Mopar fender tags" and you'll see a bunch.
So, would this stamp have had something to do with not having those little square tags they put under the screws that usually have the number/letter stamps on them?
If the factory didn't have any of those tags left, then they would have just punched the fender tag?
Somebody likely knows the answer but it's not me. I just double checked and I'm surprised to see that this is an LA tag and mine is Hamtramk from the following year and both have the "10" on them. I was expecting to see that they were from the same plant.