spring-overs range anywhere from 4.5 to 6.5 inches or more. the outright lift varies because of axle tube thickness, leaf pack thickness, and perch height. How much lift you need up front to compensate depends heavily on the sag of your leafs. are your leafs stock?
to measure your lift over stock: http://comancheclub.com/topic/11098-how-to-measure-ride-hight/