John, that is very nice of your nephew to make drawings of the firing pins. The only thing I can add is that in Brohpy's book "Plans and Specifications of the L.C. Smith Shotguns" there are no drawings for individual gauges meaning that the firing pins for a .410 to 12 gauge Featherweight guns are the same. For the Regular frame guns there is a slight difference in the overall thickness as shown in your one drawing.

To see the dimensions, hold control and hit the + key until you can see it clearly. Don't forget to hold the control key and - key to go back to the original size