This is extent of my knowledge....
YJ springs will fit on rear...
But are wider than fron CJ springs so new spring hangers needed.
I have HD rears all round on The 1 Tonne they give a good ride.... Your choice as to spring over or under....
Cheap at £100 a corner .....compared to £1000 for RE lift kits....
x2 YJ springs should just bolt in rear and are same width
YJ fronts are wider and longer, shackle hanger will need to move forward, conversion shackles are available.
I have Rubicon Express kit which is bolt in and works well but is lifted over stock. Apparently BDS is good too
Fit springs first and then buy shocks with the right compressed / extended length, available in uk from Suzuki specialists. Weirdly, you want the softest, cheapest shock you can find for leaf springs, not gas charged as they'll be too hard.
Don't buy cheap leaf springs you'll be nursing your back!!