Here are the photos I promised
The first two are the front passenger side suspension from front and behind. I suspect a new strut/spring that was 2-3" shorter would work. The driveshaft currently hits the wheel 1 1/4" lower than it leaves the transfer case, so a 2 1/2" lift would just be the same angle reversed.
The third photo shows the back suspension spring and shackle - a longer shackle would give a drop and there's 2" of room above it.
The fourth photo shows there's a metal spacer block giving 2" of lift. I can remove this block and snug the nuts up. I noted the thread stops just short of where the bolts would be, so I would need to tighten four more nuts onto the back of these nuts so there was good thread supporting it. That's more secure than using a bunch of washers on each one.
So, I see a clear free way to get a 2" drop at the back, and a 4" drop if I replace the shackles. I also noted while back there that the dampers were original and need to be replaced. I assume this is true at the front also, so that is my excuse to get new dampers/springs at no additional cost.
It's not an immediate project, but when I do it, I will remember to re-align my headlights, since the truck will be lowered more at the back.