On the 3" or 4" problem.
I have a set of the Currie Sportsman leafs. They are not on the XJ yet as I am working on changing gears.
What I can tell you is that where my 100k+ 94 leafs are 49.25" eye to eye, unladen (practicaly flat, can't get any longer) and my RE 4.5 leafs are 48" eye to eye, unladen. The Currie Sportsman leafs are 50.25" eye to eye, unladen, and without the boomerang shackle, will bind the stock shackle at this unladen length, and heaven help you if you were to try and compress some of the arch out of them, making them longer still! So this 3" leaf (if thats what Deaver is claiming) pretty much has to be run with the boomerang shackle that gives it another inch, therefore, 4" leaf kit, with shackles.
I'll be able to tell you more when they are mounted and broken in, just observations at this time.