I purchased a rear addco sway bar last January for about 250 us plus shipping as I'm in Canada. The sway bar was installed about 4 months later. I had the black version which I think is version 3 of the rear sway bar for the WJ series. I used the large washer install method as described in jjeeps - the unit had no knock or rattle after the install and worked great .
Other things I did for the install, I used the supplied bushings but cut groves in them for grease passage and lubbed the bushing before placement with special non slip black marine ( mercrusier bearing ) grease as this grease will not wash out with water.. Normally it is used on outdrive lube points, so its gotta stick around even in water fresh or salt. No problems encountered with that setup.
I had previously put a set of oil sprung shocks (skyjaker 7000's) into the truck that improved the handling greatly. With the addco sway bar mod I could feel an even more responsive feel in the handling of the truck and that was just backing out of the garage! (it did not wobble over the garage floor lip anymore)
What a change to the handling round corners! My 99 had a tendancy to top wobble around corners forcing me to slow down a lot , too much for the corners. I had the feeling that the truck body would slide right off the wheels in any corner.
The addco mod made the jeepGC handle more like my car. I could not go faster around the curves but because of the new handling I did not need to brake before during and after a turn in the jeep. This mod changes the rear end by pinning it in such a way that handling changes for the better with respect to stablity, smoothness and road handling around curves or in any s manuvers.
If you do mainly road driving like I do, 90% or more this mod is great. I did find though on a little bit of rough stuff ie even uneven dirt roads this mod is not what you may want as the tail end is too pinned and the ride becomes progressivley rougher with higher speeds -- even with soft shocks.
I highly recomend his mod to all the street drivers like me who would like to have more decent handling in corners and generally in the way the truck handles all round... a really great mod