You should message a member called "gangstarr", he purchased an extra set of SL springs when he installed his, I think he just called up Superlift and ordered a set for like $100. You could also add a rear 2" lift spacer in conjunction with the OME springs, like CoreXK; I have some daystar spacers you can have for free, just pay shipping.
Either way, I ran used SL springs for a year or so before I sold the XK. There are a few things to consider, as Sal said:
1.) Longer rear shocks, I used F-150 Monroe load levelers ~$100
2.) Longer Bump stops, most use body lift pucks\extd. bolts + stock bumpstops
3.) Longer Swaybar links
Some use extd JBA quick disconnects, or don't run a swaybar at all. I first used a set of used extd SL swaybar links, but upon hitting a rut hard while off-roadin', the link was able to make contact\dent the lower control arm. I ended up runnin it with no swaybar after that, and the jeep handled just fine, with max travel all the time, this works great with the load levelers.
4.) Minor trimming of gas tank skid
Need to cut out roughly a 4"x4" section from the top of the gas tank skid to give clearance for the driver's side lower control arm. Not too hard just a tight work area, I used a handheld hacksaw.
5.) Rusty's adjustable taskbar
This really helps the driveshaft keep clear of the gas tank while flexing. Matt has a pretty straightforward install write up.
Adding rear Superlift springs put the rear an inch higher then the front, which was OME HD struts\springs + 3/8" spacer. I think the rear measurement was ~39" ground to fender with worn 265/70/17's.
Good luck sourcing and installing the springs, they definitely give the XK a ton of lift for a fraction of what the whole kit costs.
2015 Pro-4x Nissan Frontier/Factory rear electronic locker in factory modified rear Titan axle/2.5"Front\2"Rear lift
Sold-2008 3.7L QT-1 dark blue Jeep Commander/3+" modified OME lift with 3/8" Rocky Road strut spacer/4" rear SL springs/265/70/r17 Goodyear Duratracs (Load E)/1.5" spidertraxx spacers/F-150 Monroe Load Levelers/4xguard matrix, front guard, belly guard, and rock sliders/Airflow snorkel/Thrush welded exhaust/
Complete 3.07 to 3.73 V6 gear swap
Powertrax rear locker
Last edited by Ross; 03-19-2015 at 09:34 PM.