2 more suggestions, 1.Coil over shocks work. 2. If you add shackle extensions
cut them off just below the first hole and round the edges with an angle grinder. I had a lot of people ask me if my car came with them from the factory because they looked so neat without all the excess hanging down.
You really don't want to go passed the first hole like Ericnova said handeling will suffer and it will stress the leafs from the axle to the shackles over time and produce negitive arc.