Have you used a magnet all over the fenders? I'd be inclined to think that someone fiberglassed over steel ones. It's a lot of work to make one-off fiberglass fenders for an oddball truck.

If they are all glass, I think they were after market repair items from the 1970s or so.

1950 Chevrolet 3100 (Ol' Roy)

1939 Packard Standard Eight Coupe (The Phantom) | 1956 Cadillac Coupe de Ville (The Bismarck) | 1964 Ford Galaxie 500 coupe |1966 Ford Mustang (Little Red) | 1969 Pontiac GTO (The Dishpit) I 1979 Ford F-100 | 1976 Ford F-150 (Big Red) | 1995 Ford F-150 (Newt)