James, I suppose if they are going to do all that work, then the 3 hours is justified. I assume they are talking about the rear subframe and the rear ride height. My experience with all this is on a '91 S-class, but probably very similar. I never heard of an alignment shop trying to adjust the rear subframe, other than replacing the subframe bushings and the diff mount. I don't really know how they would effect an "adjustment" other than just replacing these rubber parts. I did have a shop actually bend a swingarm on my old Cadillac to get it in line, but it had been hit. Concerning ride height, my rear sagged a bit (the car's rear) and I installed some slightly thicker rubber spacers above the springs (MB makes 3 sizes). This brought the height, and the rear camber, back in line.
That may be what they have in mind. Is the rear low? do the rear tires lean inward? Then you probably need the thicker height spacers.
After I raised the height, and replaced the subframe bushings, all has been good, the rear stays in spec, and I pay for a std alignment on the front, about $60.

DG