No such thing as original. The only fuel cap found on F100/350's prior to 1967 is located on the in-cab tank's filler neck.

Take a look-see in any Ford truck parts catalog, see if you can find a fuel door listed prior to 1977 (1977: First year Styleside/Flareside had fuel doors). Lotsa luck, cuz there isn't one.

9' Express Styleside bed exclusive to 1957/66 F350's / 9' Express Flareside bed exclusive to 1953/66 F350's.

Aftermarket fuel tanks usually have the fuel cap located behind an aluminum or steel fuel door that is riveted to the bedside.

 

From the looks of the VERY small pictures I think you have a 57-60 styleside bed. You can look at mine in my garage or gallery. It would help of you posted bigger pictures.

That being said, that fuel door was likely added sometime during it's long life. Not original, but if you plan to locate the tank in the back like many of us have, it may be very handy.

 

I found out how to make the photos bigger.



I'll take a few close up shots tonight and post them in the morning.

 

That is a 57-60 bed that someone added a fuel access to.