Chevies make good add-a-leaf's for using pretty much any other 2 1/2" spring. But on a runner they work good. DO NOT use double shackles if you want to keep the rig upright on the trail. Run a single shackle with a the shackle hanger reloacated back about 4" with a 5-7" long shackle and they'll be good.
Uh oh... ive got dual shackles with chevy's.... Sorry to hijack..