[Richard]

The most secure method is to get caster shims that bolt onto the spring pack with the center pin. They are available. Just looked at some spring shims I recently purchased for another use and they have the smaller hole for attachment to the pack.

Add with edit- The Skyjacker 8" lift springs I used on my last truck had the shims pre-installed on the front leafs to alleviate driveline angle. The decreased positive caster was a compromise I had to live with. Are you trying to increase caster, yes do it. There should be no problem with the CV clearance or driveline angle with the 2.5" springs. IMO if you are installing the shims to angle pinion up for the driveline, there is no reason to do it. After install of springs jack up truck put on stands and let axle hang. If driveshaft spins freely you are good to go.