Hy 69Cuda, just to clarify, the change in wheelbase occurred between the 56 and 57 model years, they stretched the wheelbase 2 1/2". I know the frame is longer from the firewall to the front of the frame but I'm not sure if that was where the total wheelbase increase took place. As to the wheel arks in the fenders, the parts book lists the same part number for front fenders on the series 6 trucks from 55B to 57, hope that helps.
