1960 bed and cross sill/ bed support issue

[scotzilla]

bought a 1960 short bed fleetside project from a guy in pieces. Ive built a few of these trucks and have had to shim the bed, body and core support to obtain a straight body line but this 1960 is throwing me for a loop. I assembled the bed with the cross sills where they go according to LMC's catalog and it looks like im missing a frame stand off or some kind of spacer for the rear cross sill as its spaced about 2.5 inches off the frame. Am I missing something? All this pics ive found on the forum dont have the 60 style frame.