installing sl trunk lid spring

Help!
has anyone ever tried to install the OEM torsion spring trunk lid opener on a 107 car? I am restoring a euro 450sl and every operation has been impressively easy until this one. I've ordered the MB installation tool for this purpose, but have doubts about the proceedure. The manual makes it sound simple but the load is about 200lb. and the quarters are incredibly cramped! Is there a trick?
David