6400 is about a 161" wheel base.
6100 and 1 ton pickups and cab/chassis used a 137" wheelbase.
No, you can't simply put a 1 ton bed on a 6400 truck, considerations are the extra 2 feet between cab and bed, fenders not fitting over the wheel or wheels, inside wheel may hit bed sides and running boards not lining up with the front fenders.
Grigg
