There is no significant difference between a 3.5" and a 4.0", and you may get more out of the lift than suggested but settle in time. A good start for 33s would probably be a 2.5 lift, and a 1" body lift. If you get vibrations in the drivetrain from the suspension lift, do a 1" tcase drop. If you still get a little rubbing, do a small (1" or so) shackle lift. At hat point, you should stay within reasonable limits before you start the snowball effect. After much more you will need "CV" (double cardan) rear driveshaft to allow more degree of bend in your shaft, which will lead to needing shims or cut/reweld spring perches, etc etc... it just snowballs from there. Also, there are a lot of people who will tell you a little lift on medium sized (33s) in little to moderate wheeling is a great combo. You may not make it over the biggest boulder in the trail, but you could likely get anywhere you needed to, and go around that boulder, and enjoy your well mannered Jeep at a decent price. Also, there's a lot to be said for maintaining a low center of gravity for stability both on the highway and the trail.
Again, all of this is theory, since this is my first CJ and it came this way with huge shackles, probably 4" lift springs, and 1" lift body... and will be replacing my shackle to a reasonable height and deciding then whether to change or alter my springs from there.. I need a more reasonable ride stiffness and a little better handling.
Some of the spring companies I've heard recommended for a CJ are Rubicon Express, ProComp and ORV. Good luck and report back as it all goes.
USN Jeep Club Hull #135 (Retired USN 1992-2012)
'80 CJ7__258, TF999, D300__'86 CJ WT D44/D30's(3.54s)__GPF custom front/rear bumpers
4" springs__33x15s on black steelies__Galaxy DX959 CB__Cage (built onto YJ "family" bar)