Thats not exactly correct...the 96-down xj's are less prone to driveline vibes...the 97+ XJ's are more prone, just the way it is...actually the reason is because of the shorter output shaft on the t-case but we dont need to get into that...avoid tcase drops altogether, it puts alot of stress on already crappy motor mounts, and should be used as a temp fix, not "until i get a sye, but its been 2 years"..a sye conversion can be done easily and shouldnt be the missing link, alot of damage is done...pinion bearings, output shaft bearings,u joints, motor mounts, and just plain annoying vibes. you should be fine with just 3" lift anyhow....
For a 3" basic lift, look for full 3" coils in front not spacers, and either a 3" leaf pack, or AAL...not blocks...or shackles and blocks...no blocks.
Atleast then when you decide to go bigger you can go to 1.5" spacers and 1.5" shackles (which will add to pinion angle in the rear) . However at that point you will also be pondering lower/upper control arm, SYE, cutout flares, lockers blah blah...start with what is going to work for you, but start with a good base, that way if you want to add on you can. If not you have a great suspension that works with 31's and no crappy blocks and spacers to deal with.
Im sure JPThing can chime in with some old hockey pucks thaty work as coil spacers for sale