You could easily drop the rea shackle length down and remount the hangers, looks like the rear axle could go back a little farther as well.  I run a 5" shackle in teh back, but stock springs and it seems to work well.  Up front you can also go down in shackle length, but may have to remount the hanger or install new shackle tubes.  You may be able to rebuild the leaf packs with some stocker springs to help lower it.

When I do my SAS, I plan on running a 3" shackle with RUF to keep it nice and low.  Out back I will be using filpped F-150 rear springs.