Rear frame supports on a SHORTWIDE BED???

[LILRED66]

'60-'62 frame rails are the same width, regardless of stepside or fleetside beds, the same is true for '63-'66. The earlier frame rails are farther apart than the later years. It appears your bed, or at least the rear cross sill, was a '60-'62 and the frame is a '63-'66, therefore the rear cross sill frame perches were cut off, as evidence by the flanges still on the inner face of the rear cross sill.

I have seen a 2" x 2" square tube, approximately 4" long welded at the end to the inner face of the rear cross sill, to suffice for the rear cross sill frame perches. Also, you can drill the spot welds on a pair of factory rear cross sill frame rail perches and install them on your rear cross sill in the proper location.

Hopefully this information is helpful.