Hey Bruce,
What's the chances of you posting the serial number that is stamped on the top of the left front frame rail found just ahead of the steering box? This might help clear up what year truck you have or what it's a mix of. The 1955 & 1956 Series 6500 were 172" wheel base trucks and the 1957-59 Series 6500 were 174.5" wheel base. Chevrolet moved the front axle 2.5" forward in 1957 to accommodate the larger wheels.
Your truck could be wearing 4100 fender numbers, but is really a 6500 (2-ton), they share the same fenders.
Mike B
