The cowl tags on Dodge trucks are found in a couple of locations:

57 tags tend to be found on the firewall, either in the middle of the firewall, or on the side of the firewall. There were two tags on most 57s, a 1 on a tag, and a separate tag that has a longer string of numbers. These tags could be on one rivet, or on two separate rivets.

58-60 tags are generally found in the center of the upper portion of the cowl, see the picture below for the location

I have yet to find any information about the meaning of these tags, there is no relation to anything that I can figure.

I did find that the 57-58 tags(the longer one in 57) tend to start with L for light duty trucks, and H for heavy duty trucks. I have never seen an M for Medium duty. Plus I saw one Light duty truck with a H tag.

Once you reach 1959 the tags just have 4 or 5 numbers, no letters, and I have no information as to what those numbers mean.

If you know anything about these numbers, please let me know!