Correct.
You can lift the rear very very high if you want to...but, your FRONT will still be down low.
A torsion bar adjustment can get a free 1.5" up front....but
higher than that, and you can't get a good alignment, and the outside of the front tires will rub off pretty fast, etc.
If you add a set of UCA from AC, they are shaped so as to pull the top of the tire back in, to correct for the camber change from the extra lift...so you can go ANOTHER 1.5" up, to a TOTAL of ~ 3" of FRONT LIFT.
IF you are ALSO getting the UCA's to do a full 3" up front...the adjustable shackles make more sense...
..but, not enough to raise the REAR a full 3" either, SO, You'd STILL need to add a set of AAL for example, to get the butt up the REST of the way.
To provide 2.125" of rear lift....the shackle would have to be ~ 7.25" eye to eye.
The latest measurements for the fixed length shackles put them at ~ 6.625"
So that makes the adjustable shackles ABLE TO extend ~ 5/8" more than the fixed ones.
(If you want balls to the wall super shackles, as far as off roading goes, get the Revolver Shackles.)
As for new shocks, you don't NEED them to install shackles, but, your rear articulation will increase with longer shocks, as your shocks will be the limiting factor as far as wheel travel with the OEM shocks...
Of course, they already ARE too short to allow full travel anyway....so they will simply STILL be too short.
:wink-big: