Lifting a truck with 3" front springs

[c Terris]

My k20 has 3" on the front and 2-1/2" on the rear. My truck is supposedly a special edition or something from the factory. A factory plow truck. It also came with a 1 ton rear axle and a corporate 10 bolt front. I'm doing a shackle flip on the rear and want to do a 4" lift spring in the front. Does anyone know what lift springs to use or how to convert the leafs to 2-1/2".