Not sure I'd recommend leaving that bushing out...
Unless the SD is appreciably different from a W123, the shock and its hardware should fit okay, boot and all. If you placed a second jack underneath the new shock and raised the whole ball joint assembly---and the car was lifted off of the first jack---then there should be PLENTY of weight applied for that shock stem to poke through adequately. Additionally, if you forego using that inner bushing inside the boot, then what will you have in there for the underside of the fender well to contact? If you have only a boot and a metal washer inside the boot directly on the underside of the car body, then it seems you are in danger of defeating the purpose of the shock...
