Pull your springs. disco your sway bars. unbolt lower shock mounts. remove upper jounce bumper cushions. Put axle at full bump. Do your tires rub? Adjust bump stops to prevent tire rub. Articulate axle. Do the tires still rub? Adjust bumpstops to accommodate. Once you have the tire clearance taken care of, now you can measure collapsed length of shocks to see what shock you need.