from what i understand the 60-62 had the "x" frame and the 63 and up were box?
right?
It's actually just the opposite. The 60-62 frame has the X member and is mostly boxed, the 63-66 design has open C channel side rails. To make up for the loss of strength with elimination of the X member, it was advertised the 63 frame was made of tempered steel. The side rails of the newer frame are also 1 inch taller in the area where the motor mount towers attach.
