rear spring re-location kits.
The 3" relocation kits puts the rear springs under the frame rails. They're a bit of work as the frame needs to be cut and the front hangars welded into the frame.
But the big question is why you want to do this. You didn't make any mention of mini-tubbing the rear wheelwells. There's no benefit to moving the springs this much if you're not going to at least mini-tub and put big rubber under the back.
I'm sure you'll find pics, instructions, etc., on other threads with a bit of searching.
