They just don't know where the caster adjustment is located. It's done by the eccentric adjusting bolts on the front part of the flat springs that attach the subframe to the chassis. Look on either side of the front chassis rails and you will see them. The lateral locating rod, beside the steering shock, should also be loosened to allow proper movement. Their alignment machine should have the correct procedures for the W108's which have the same suspension as your car.
When doing the adjustment, the threaded bushings in the upper outer kingpin mount can be turned for fine caster adjustment, assuming it's not frozen and the car has been properly greased otherwise the front kingpins need to be service/replaced. The transmission crossmenber will need to be loosened as will the center driveshaft support. While the caster adjustment is done the complete subframe will move front or back and the trans crossmenber needs to slide the same way and the driveshaft will need to move too. Their all connected.
