"Even without the modified carrier I think you'd be going some in road use to actually compress the suspension far enough to be a problem (unlikely not impossible!)"
From my experience with the old carrier I'm not convinced by that to be honest. Take one "not particularly light" driver, corner weight the car, later add a passenger and then drive along a standard British road (i.e. not exactly smooth, with the odd small pothole). End result = more clonking of de-dion against the old carrier than I ever got 1-up on track.