sorry my gears are turning cause I have but longgggg hard thoughts into this for years
To ballance out the look of yours and to improve storage you might consider a roof rack over your cab. Make it an external roll cage is your best bet too. Many expedition campers have this anyway. This will functionally balance out the odd look of lower cab than camper box.
Another way to functionaly clean up the look is to steal from Merex their idea of a sheet metal perforated (alluminum?)l shell that hides some stuff in the back of their cab. On yours though hook it to the camper box? to make the box look more squared off to the cab. Can tuck some stuff into there too for storage.. or high mounted small Gen set??
Small Hellgeth version is orange in this picture.found here; its orange in this picture.
or Merex's larger version of this idea
Hellgeth's version is actually a ROP (Roll over protection). Could some contortion of that at the back of your cab on yours too encorporating a Rop. Impartant even for a non hardcore rigs. Cranium protection for family or you not real good in those old FC's
Consider and external roll cage skeleton for you Camper Box too.
As to the roll off on rails.... its been done. A Fuso 4wd and they installe a hydraulic tilt bed like used on roll back wreckers. It was a SWEET setup.