With lift springs, no shims are typically needed with the stock single-cardan shaft, however, with the 2" longer shackles, you generally need about a 2 degree shim to tip the pinion down:
- http://www.4crawler.com/4x4/ForSale/Shackles.shtml#FAQ12
- http://www.4crawler.com/4x4/CheapTricks/Driveline-101.shtml#FixingProblems