In my buddies runner we started with 1/2 ton chevies with single shackle and then we swapped 3/4 ton chevy springs for the added weight in the rear of his runner ( bumper, roof rack, spare) I have the 1/2 ton springs in my truck with dual shackles and I have about the same lift as him (5-6") . He has a 3" block as well and I have a 2" block. Hope this helps.