Number of cross sills in a '65 GMC SWB bed

[OregonNed]

Hello, I am trying to help a friend reconstruct his bed in his '65 GMC short fleet side. We are trying to figure out the number of cross sill, and the sizes of each. From a few photos I have seen, it looks like in front of the rear wheels there are two - one "taller" cross sill, and one shorter (that would mount to the real wheel wells) - then one between the real wheels and the rear cross sill - (for a total of 3). Could anyone confirm this, or have a picture of how these are set up? Thank you, very much appreciated!