http://www.tcklineracing.com/webdocs...Details421.cfm
If the above are the FCABs you're talking about, you might call TCK and ask if they're centered or offset. I believe that they're centered, which would be appropriate for the E46 M3 but not for Z4M. See post #55 in this thread
http://www.zpost.com/forums/showthre...=571912&page=2 for discussion of using a centered bushing...short version: changes caster angle requiring camber plates to correct, and then leaves you with tire clearance issues courtesy of having moved the tire rearward in the wheel well.
While you see these advertised as fitting the Z4M, along with others such as Treehouse, they don't. To my knowledge, no one makes a proper offset upgraded bushing for our cars.