I have a '79 K5 with a 4" lift and a 3" body lift. I am going to put a 6" Tuff Country Suspension with ORD shackle flips in the rear. I have a 14 B FF in the rear and am getting a D60 for $600 for the front. What size shims do I need to go with for the rear. All I can find is a 2" or 6" shim. Can you guys give me some advise about the right size shim I need. Thanks for all your help guys and gals.