As mentioned above, make sure there threads are clean. I used my Dremel and a soft wire brush attachment on low speed to clean out the threads on the coilover body where it meets the adjustment collar because I had a bunch of built up dirt, and then hit it with some WD-40.
I also separated the LBJ (which allowed the coilover to fully droop) and swung the spindle out of the way using a bungee cord to keep it off to the side. Also I used a large Allen wrench to help crank on the adjustment collar along with the spanner wrench, which gave me more leverage since the spanner wrench doesn't give you much room to really crank on because of the design.