For the 98+ you do not buy a specific set degree shim. You actually replace the upper control arm bolts with eccentric cam bolts
that allow infinitely adjustable camber and caster. But your definitly going to have to do it on an alignment rack, or have the alignment done. And as a warning, rangers don't always go back to perfect camber even with the eccentrics.
The only way I've seen to go back to perfect is using DJM's 5" grand slam kit. This is because they give you upper and lower control arms that are different lengths than stock and correct the camber and caster.
I used 2" drop springs from DJM on my truck, and I can't get back to perfect camber, and my ball joints are at about the end of their travel. I think this is the maximum you would want to go. I can't imagine how messed up the 3" kits are making Rangers.
Let me know if you would like more information.