Originally Posted by maboyce

...and measuring instrument 126 589 08 21 00. These are for working on late W123 and W201 differentials (at least), those without lateral bearing caps. They apply and measure horizontal stretch to the differential housing to allow the large c-clips at the sides to be removed and installed correctly. These are my reverse-engineered plans for tools of equivalent function. A welder is definitely required, and I used a metal lathe. A drill press will work as long as one can find a properly-sized piece of round stock to press on the differential. The only really critical dimensions are the location of the screw and the location of the holes for bolting the tool onto the differential case.

The measuring tool is also useful for earlier differentials with lateral bearing caps.

Construction of the tools is described in my car's build thread.