[Stormin08]

they make shackles, but typically they are longer and would lower more.

going shorter would drastically change how the spring flexes and cause a bucking more that likely.

you could consider a rear shackle flip ??? depending on your fab skills and which holes you use...

dig through some 4wd threads, or service sites for rear shackle mounts...some make a boxed version that are smaller overall than a stock and could easily be placed where needed.