Well I did a little measurement confirming what I suspected after posting the original post and reading some responses.
My 39 bed is 48-1/2" wide without the script tailgate. I would make the assumption at this point that the bed and tailgate are from a 41-46 truck.
That leads to a few more questions. My rear fenders are about 12" wide. As I recall they come from the 40-46 series as well. Correct?
Finally that leads to another question. How do I tell the year of the frame? Does the 37-39 share the same frame and the 40-46 share frames too? :confused:
All of a sudden my mostly "original" truck doesn't seem so original any more!
Thanks for all the great help.