if i read this article correctly you dont really want to inc. the rear sway bar as the xfire oversteers to much already correct? adding a larger front sway bar will help the overstreer. maybe m/b made it tuff to remove the rear sway bar for a reason!!

max on jhm2k's white coupe that mr. mopar has theres a slk32 amg front sway bar that measured 28mm. bet you could get it for cheaper than the h&r unit and your only 2mm difference
How sway bars work