I'm at home away from my work computer with my drawings, I believe their may be even more crossmembers I know I ordered 22 96" 2x2x.187 today, the rear cross on the back is 2x3x.187 and I'm sure I might have missed one or 2.
The box is 22' long with the 2x2's on 16" centers. that gets me roughly the 14 for the floor, as 2 of them are almost atop each other where the floor drops the 11". The other 6 will go under the frame. 3 in front, under the cab and transmission. The other 3 or 4 will go under the fuel tanks and generator behind the drivers.
In case you are wondering, if I should ever need to drop the trans out the bottom, I will just sawzall the tubes. I think it would be easier to just pull the engine and trans in one shot then split .
after typing this I think you are referring to the The factory cross-members on the truck frame. I had 4 behind the cab but I removed the far back one and replaced it with a heavy steel box to hold my water tank. if you need another factory cross-member, I have one laying on the floor next to my mess. You could use it as a boat anchor.
