KWIG61 - First off, Welcome to Stovebolt!
I was unable to find any history of Protect-O-Plate decoding in Stovebolt threads of the past, but did find a couple of thing that might be of help from the web.
Below is a zoomed in view of a pic of a 1965 C10 Protect-O-Plate I found on ebay. If you squint a little, you can see the lighter shaded printing just below each of the typed character sets. The upper left is for the vehicle paint code, then upper right is the VIN. The center section is the owners name and address (at least City and State). The two lower left characters sets are the engine ID code (1 letter for the assembly plant followed by a 4 digit number which is the month and day built and the engine 2 letter ID code, followed by another letter which I'm not yet sure of what it indicates) and below that the rear axle ID code (2 letters for the axle ID code followed by the 4 digit month and day built and the single letter for the plant where the axle was built, also followed by another letter which I'm not sure what it indicates). The lower right spot is for the transmission ID code (one letter which indicates the model of transmission followed by the 4 digit month and day assembled).
I haven't yet found what the transmission letter designation indicates. Still searching on that. I have found the 1965 codes for the engine and rear axle, but will have to wait until tomorrow to add those info sources.
One added source for some details on the Protect-O-Plate decoding where found in this
same subject thread in the 67-72chevytrucks.com forum.
If you post a picture of your plate or the stamped details we can take a stab at decoding it for you.
