the shims set 2 things, caster front and pinion angle.(both ends)
and what to do varies by lift height, stock springs, zero lift, and more , after market springs.
do not run 0 caster, in front ever, 6 is natural up front. for safe steering.
mine are 2" lift new springs. (and)
zero shims front and The welded on C to C knuckles are 6 degr factory set (hard) front.
and the rear springs new,had small shims in the kit, that tilts axle pinion up just a tad.
the factory car has a choices of leafs. based on things like snow plow option and more. as Pman sad so clear.
what you have are going to do , not told.