i think with shackles you'll only get about 2 inches at best but 2 inches but with larger tires you could get to the 3 inch mark... lift blocks may work like Lowsuv suggested but i don't like them period... you increase the possibility of axle wrap (although that may be more predominate with a drive axle?) that being said most 4x4 trucks have them from the factory so take my opinion for what it's worth. i don't know of a reason that an axle flip would be bad other than it being lifted too high. (my axles are below the leaf springs from the factory) the subframe idea seems pretty good but unless you really trust your wielding skills, you're out of the realm of DYI.... good luck