The upgrade as far as OEM parts goes is (I believe) the Z3 reinforcement plates along with the e46 shock mounts. I went the easy way and got the RSM's from Rogue Engineering (no reinforcement plates needed). As far as installation, it's really easy. Just remove trunk carpeting, jack up the car, pull out the old shock mounts, throw the new ones on. The Rogue ones come with instructions and a diagram.