The beds changed from 9 boards to 8 boards in mid 1951. I'm not sure what that would have to do with the header panel though.
I have a '49 one ton with 9' bed, but I'm not near it right now to take a look.
Check Mar-k's product and see if you find the same thing. They make their own in house.
What year is your bed? Is it 8 board or 9 board?
