I used a six inch C clamp and it worked fine. You really don't compress the SuperSpring very much while adding the rear bracket bolts. It is a very easy install. The hardest part is jacking the truck off the ground while not putting the jack under the axle.
2014 Eagle Premier 361REQS
Mor-ride pin box
2013 GMC Sierra 2500 CC SB 4x4 Duramax