There is no uniform pattern for the plates. I have seen plates punched with all 1/4" letters and numbers (like the '48 plate) shown below.
https://www.flickr.com/photos/advance-design_parts_co/8130544334/in/album-72157631870734114/I have also seen them punched with 3/16" numbers and 1/4" letters (like my own '50).
https://www.flickr.com/photos/advance-design_parts_co/8129122101/stats/Here is another from a truck I parted.
https://www.flickr.com/photos/advance-design_parts_co/8130515931/stats/I believe the plates were punched prior to assembly with general year/model schemes and then the final plant production number that day as produced. There is wide variation in the spacing, and location on the plate of the various schemes. One final caution the stamps do not require a hard hit, it takes practice to not cut the plate with fresh stamps. I perfected my technique on a piece of sheet metal I had in the shop (stamp it on a block of wood, not metal), I would suggest practice before damaging a $20 plate.
If you look through my Parts and more parts album and my Parts Trucks album, I have many examples of plates off my parts trucks.
https://www.flickr.com/photos/advance-design_parts_co/albums/72157631868452754https://www.flickr.com/photos/advance-design_parts_co/albums/72157631870734114
