Firstly, world of difference between the spring over 10pk Greg offers. Converting to a spring under set up allows for more articulation/travel and is a much more progressive set up. Secondly, the 62" pack can be set up anyway you like...you can get close to 5-6" of lift probably depending on your shackle length. Additionally, the 62's can be set up under the frame with custom mounts...however; without moving everything outside of your frame you will need to relocate your gas tank to allow for the shocks to come up through the bed.
My truck is currently at Giant getting the 64" race kit installed. So far we have had to build a custom length shackle to clear the body mount on the bed and the rear bumper had to be removed.
Unless you are intending to actually PreRun, Chase, or Race your truck then honestly I think your money could be better spent elsewhere. Greg's 10pk along with a set of 14" shocks can get you a very nice comfortable ride in the desert. The nice thing about going that route is everything is bolt on for the most part and there is no guess work.