In 1957, Ford replaced all the 1953/56 Flareside related parts with 1957 parts....including the rear fenders.

There are TWO different 1953/79 Flareside tailgates:

B7C-8340700-A .. Flareside Tailgate-49 13/16" long / Use with F100 6 1/2' bed.

B7D-8340700-A .. Flareside Tailgate-54 13/16" long / Use with F100/250's 8' bed & F350's with 9' Express bed.

 

Thank you and the one pictured started life as the 50" as the 55" ones are way taller, unless they cut that down too