I just got off the phone with Rob at UUC and had an interesting discussion with him.
It appears that the rear bars in their kit, shown below, are guaranteed to fit the Z4Ms because their part number is an exact cross reference to the E46 M3s.
http://www.nexternal.com/shared/Stor...t=products.asp
However, the same doesn't apply to the front bars. He offered to sell me the kit, and take a refund on the bar if it doesn't fit, as he is interested as well if it will.
Anyone have any experience with this? Is this a decent risk to take? Would running a rear-bar only have negative effects if the front bar doesn't fit and I have to find somewhere else to source it from?