You wont want to run the springs under the rear axle. this will cost you a lot more money than simply building a pack to get a few inches of hieght to match teh BJ spacers up front. To move th esprings under the truck you will have to weld on new mounts under the axle, and then buy 3" lift springs to compenstae for the springs being under the axle. Building a set of springs to gain a few inches should run you less than $30. Get a set of Chevy(non-63's) and a couple of new center spring pins, use the longest leaf(non-main), from the Chevy pack and install it below the main on the toy pack, this should give you about 1-2" of lift w/o stiffening the ride likw an add-a-leaf will if you aren't carrying extra weight in the bed. Your origninal u-bolts should be long enough to accomodate 1-2 extra leaves before needing to buy longer ones. You should be abole to install the BJ's and springs for under $150, though you will want extra money for new ball joints(if you don't know the age of the currents ones), shocks $100-whatever you want to spend.