I'm not certain, but it looks like the sides can be locked out in the horizontal position. If it needed to be driven that way, I bet those bars hinge out to match the "new" width of the truck to give the driver some idea of what room they needed to have on the sides.
Some of these uncommon mods might have been done by the factory, but some may have been done by the services that used them.
I can't put my finger on them right now, but search for Pinzgauer FLA (Fliegerabwehr) and you'll find some super cool Austrian anti-aircraft 712s with fold-down sides and cab