The general rule is if you make a shackle like 1 inch longer, it will lift it 1/2 inch depending on shackle angle. to get 2 inches out of your jeep you will need to make the shackles 4 inches longer if the angle isn't too much. You are only lifting half the spring.
Shayne, i made my own shackles out of 3/8's plate. I cut them with a torche, grinded the edges and then drilled the holes out. I think mine are like 9 inches eye-eye or close to that.