Of all of the '60-'66 Chevy/GMC truck fleet-side beds, we have disassembled, I have never seen any evidence of spacers, of any sort, between the landing pads of the bed cross sills & the landing perches affixed to the frame. Although metal-to-metal, is recommended, a square of sound mat, like Hush Mat or Peel-n-Seal, is a good isolator and the thickness is minimal.
