looking at your pictures, how high your truck sits right now.
I would be (and am thinking about it as I just bought the 3 inch springs for my wifes truck) moving the upper shackle mount up into the frame. Longer shackle and no added lift.
weld in some tube the correct size for the bushings.
maybe cut the thin inside part of the frame and replace with 3/16 and plate the out side also. moving the in side part in far enough to be the same width as the shack mount.
or just plate both wides and make an off set shackle simular to the front one. wide at top and standard at the bottom.

Any one see anything at all wrong with this idea?

heck I may do this to my truck also. longer shackles would help me with droop.