John,
One needs to bolt a fitting plate at the bottom of the B pillar if following MB's bulletin. I have a very late 230 and I had to drill a hole at the base. No big deal at all given how much safer the car is with 3 point belts and, of course, entirely hidden. That is unlikely to be the deal killer for you. No, the real deal killer I imagine - having seen many photos of your car - will be that the belt doesn't fit between the B pillar upholstery covered steel plate (the fairly chunky piece of curved metal that goes over the B pillar) and therefore must have a small chunk cut out of it (about the size of a fag packet) in order to allow the belt to move freely. This was a bit painful for me. When I peeled the original upholstery from my B pillar steel plate, I found the original part inspectors wax crayon marks from the factory, as I am sure will everyone else who has not delved into this area before. I had to cut into those, typically. However, it's done now and I'm all the better for the belts being in the car.
JH