Those shims set a baseline for caster only, and are also used to compensate for non-straight construction (typical in both 122s and 1800s). You'll often find more on one side than on the other. The also lower the engine relative to the body without changing its height above the crossmember.

The actual caster adjustment is accomplished by using odd numbers of shims in the front and rear points of the upper control arm. More shims on the rear bolt increases caster.