Hey Chevy6400,
You are correct, some of the 1957 Series 4000/6000 parts are unique to just that year. All wheelbase of Series 4000 & 6000 models were lengthened by 2-1/2 inches, to provide for the use of larger tires without causing interference between the wheel and the toe board on extreme turns. For 1957 the front axle is moved forward on the springs, shortening the front overhang. In doing this the front fender wheel openings were increased from about 39" to 41-1/2" (measured across the bottom). Other than that the fenders look just like the 55/56 Series 4000/6000.
As Calvin mentioned the Hood is '57 only, while the Inner Fenders, Cab and Doors are the same as the pickup's (55-57). The Series 4000/6000 Core Support, Grille bar and Upper/Lower Grille panel are the same (55-57).
NOS fenders are still around...I just saw a pair at the ATHS show in Auburn, ID. They went for about $400 for the pair. I sold my last one at Hershey last Fall. Keep watching eBay and your local swap meets.
Mike B
