Continuing to do homework on this, I found a great website that showed many vehicle spec options based on the VIN:
http://www.free-vin-decoder.com/. For my 2006, it showed each of the 4 suspension spring groups (zxx) that are paired with Mopar part numbers on most Mopar part websites. For my 2006 Sport 4x4 CRD, these are the Mopar spring numbers based upon the decoded VIN z groups:
- Front L 52128880AA (zck) <-- discontinued
- Front R 52128879AB (zrj)
- Rear L/R 52128870AA (zcu,zru)
I was not expecting to see different front left and right springs -- perhaps it is due to the extra weight of the 4WD transfer case, front differential, and battery on the driver's side? The Front L spring shows as discontinued so it looks like going stock is not a viable option FWIW.