Mopar Performance shims are steel, you may need to order addition degree shims seperately, along with the shim kit, IIRC the shim kit has 6 shims (3 pairs) 1,2,3, degrees each, and 1,2,3, are available seperately, your only going to use them to fine tune the pinion angle, as it would blow to have to reweld the rear perches several times...I know ideally your looking to have the pinion windup to 3 degres max UP in your application, but it's best to "work" the pinion inclination "UP" to desired point, rather than overshoot the benchmark, confirm the pinion angle by measuring every time you add more shim, then when you feel you have reached the ideal pinion angle (by driving the car for driveline "feel"), record it, I would then cut the perches, weld new ones, but do it in the car, otherwords mock up the axle in the car with the perches/axle bolts/etc/etc and tack weld the perches with the car loaded on it's suspension, and the pinion rotated to the desired installed angle....then remove and finish weld the axle

Mike