A ZJ lift is nothing more than this:
1)taking a set of 1993-1998 V8 grand cherokee front coil springs and putting em' where your fornt springs are
2) You then either put your front springs where your rear springs are to level it out, or use the Ford Crown Victoria rear springs in your rear which does virtually the same thing.
I put my fronts out rear and am within 1/4" of the front. I did buy new Moog front coils for $92, they are very very stiff coils but ride very nice with my skyjacker nitro shocks. I don't even have a front bumper on right now to add weight and make them smoother. I doubt they will droop with weight since I'm 300lbs and can stand on my cross member and it only slouches 1/2 inch...smooth and tough.
Yes, you will definitely need a track bar to recenter your axle. Adding 3+ inches will pull your axle to the drivers side of your Jeep, so an adjustable track bar will solve that problem. Longer bump stops for the rear are necessary also.
You may also get vibes with this amount of lift. I tried to stay away from the vibrations by using this lift, but with this combo and a body lift I still got em in the rear. You can get a set of rear upper adjustable control arms to dial out the vibrations without going with a SYE. I'm lucky with a rubicon I don't need the SYE.
This setup worked good for me whie I was researching my ultimate goal. I am now taking this setup off to go Low center of gravity, and will be running 2 inches of lift with 35 inch tires. Going highline fenders. Good luck. I may throw the moog coils for sale on here (only 700 miles on em').