The shims are available from NAPA, around $5 if I remember right.
Something to watch for is locating the center pin of the leaf springs back in the center hole of the axle. If the center pin head is short, it might not hit the axle once the shim is in place. Mine was real close so I moved the shim backwards so the center bolt fit in the axle a little bit more. It all works fine, just beware when its going together.
If you have lowered the truck, front or rear, or raised it for that matter, the factory caster dimension won't work. Just add one or two degrees more then you have now. If you get to much, you will be lifing the front end of the truck when you turn. When its right, the weight of the truck will bring it back to center.
Joe
