It appears that you have a pre-54 bed. The 54 bed has flat top rails and yours are angled. If you need bed parts there are plenty of places, such as LMC, Brothers and such. Just tell them you have a pre-54 bed.
Early script tailgate, also. The BEST place for bed parts is Mar-K http://www.mar-k.com/ Go to their website, you'll find all the info you need. Rihc
If it still has the original wood in the bed and it has 8 metal strips it's 47-51 and if it has 7 strips it's 51-53. Hope that make sense.
Mack Products in Moberley MO should be able to help you with everything you need, sheet metal, hardware, assembly bolts, etc.