Here is the blueprint of a 1960-1962 X-frame
http://i867.photobucket.com/albums/ab240/c10apache/60-62frame.jpg

And here is a blueprint of a 1963-1966 frame.
http://i867.photobucket.com/albums/ab240/c10apache/63-66frame.jpg

Dimensionally they are almost identical at all mounting points. The biggest difference other than the X reinforcement is the 1960-1962 came with torsion bar front suspensions where the 63-66 had coils on all 4 corners.