Shocks that are simply shocks are not load-bearing. They only resist compression and rebound. Many manufacturers offer shocks with either springs added over them, or an internal air cylinder. These will help level a vehicle that's rear-heavy.
Over the years, Dodge had Short Wheelbase, Long Wheelbase (those had same rear overhang) and Long Wheelbase Extended (extension behind rear wheels). These were the 15-passenger "church vans" and they were skittish on the road. By all means stiffen the rear. Sway bar and maybe track bar too. Just remember you're working with a design that proved problematic.