I'm somewhat confused by your description but thats not a shackle lift.You kind of contradicted yourself there because the block will either go between the spring and the spring perch on the axle OR between the body and the frame.
A block lift isn't hard to do at all, just find some 2" aluminum/steel blocks, cut them to roughly the same length/width of your spring perch and drill a hole for the end of the centering bolt on the leaf spring. Toss them in between the leaf spring and perch and you're done.
A body lift is when you have pucks or some kind of block between the frame and body. You have to lift the body off the frame a little, remove the stock body mounts or add to them with larger ones.