This link explains, in detail, what is necessary.

http://www.peachparts.com/shopforum/mercedes-benz-tools-reference-library/178104-qp1000-torsion-bar-saver-w123-w126-s-class.html

You'll need to bring the vehicle to a certified welder to be able to do a proper job on the heat treated swaybar.

You'll also need to prep the swaybar by cutting it to a reasonably accurate length.