I agree with CrazyL, and 1fastc10, if you plan on racing your truck, the spacer blocks will cause more leverage on the spring pack causing spring wrap = less traction & axle hop.
If racing this truck... why not go with a design that is better for it?! Just like CrazyL said, throw a 4-link, ect under that truck!!!
If $$$ doesn't allow a new rear suspension setup... you may want to look into putting on a longer shackle (this will cause the back of the spring pack to move up and lower your truck by 1/2 of how much longer the shackle is over the stock length. If you installed a shackle say 4" longer than the stock one, it would lower your truck by ~2") Keep in mind that this will change your pinon angle, if there is too much of a difference, you will need to use shims to correct your pinon angle.
Another idea is to just move your complete spring perches up on the frame. Just take measurements and keep everything lined up.
Good Luck
