mancini or jeggs leaf spring xhd 340duster

Thanks everybody for the input. I plan on leaving the torsion bars at the moment but im sure I will re-visit after a while. I have 14" rally wheels with cooper cobras which I hate because they are tiny and the previous owner made the choice. I was thinking 275/6015 in the rear and 245/60 15 in the front would work with nice. Why the lowering block? Is it too high? Sireland67