bought a 3 inch lift on on e bay. rough country 250$. came with everything, steering stab. sway drop, drop pitman arm and lower control arms. guy went with bigger lift but used rear add a leaf. can i interchange with any other model? i really want 3" springs, not add ons. Im having a hard time finding them without being with a lift for under 500$ for th xj but other makes and models are everywhere???? is there anything else im going to need, want before i sideline my daily driver?

There arent any other spring packs that are a direct fit for the XJ. You can keep the main XJ leaf and fit leafs from other trucks with the same width leaf under the Xj main leaf. You can also buy just rear springs from lift companies without buying the whole lift kit. Any of the aftermarket lift companies would be glad to sell you rear springs, they just usually dont advertise individual lift pieces. Just as example, I know you can pickup a new set of Rancho or Skyjacker 3" lift springs for around $300. Look up those two companies along with Procomp, Rough Country, Superlift, 4 Wheel drive Hardware, Quadratech, BDS, Fabtech. If you want to spend more for a real good quality rear spring you can look for Rubicon Express, Old Man Emu. The list really does go on and on and they will all sell you just the rear springs if thats all you want.
You may want to start considering a slip yoke eliminator and CV rear driveshaft. XJs (especially from late 96+) are prone to rear driveline vibes when lifted. At 3" of lift, its really a crap shoot whether you will need a SYE or not, just be aware you may. You may also want to think about a front trackbar relocation bracket or adjustable trackbar, its really optional and not needed. I wouldnt even worry with the drop pitman arm. You shouldnt need it at 3" and the stock old ones tend to be a PITA to get off.
All thats really "needed" to get an XJ rolling on 3" of lift are the springs or spacers or blocks or shackles or AALs, (whichever method you choose to lift), everything else can be handled on an as needed basis.