Originally Posted by Army

I'm not convinced you'll get very far with this - but if you can measure the length of the spring as it is now and make some rough measurements of the angle of the spring relative to the lower conrol arm (LCA) and the angle between the upper spring mount and where the LCA meets the chassis you should be able to get a rough idea of how much rubber you need.

I'd do this for you but the measurements on my W123 probably won't help.