truckernix is correct, the shorter leaves do nothing to support the truck until there is a load placed on them. I was also told this by St. Louis Spring who builds the new packs sold online by most the major vendors. You can de-arch the shorter leaves or remove them completely.
Daves46pu, I am probably the one who posted what you read. Stacking them on top of the pack in the rear will lower the rear by ~1/4" (the thickness of a single leaf) for each leaf because the axle rides on top of the leaf pack. You are essentially adding 1/4" spacers between the axle and pack. Same idea as a lowering block.
Adding them in front does nothing because the axle rides below the leaf pack...however, removing them in front will lower by about 1/4" for each leaf.
