Mitch,
I believe at one point, in lieu of changing the bushings, someone replaced your steering coupling. The early cars had a coupling not riveted (as you were expecting?) with interchangeable bushings. Later models, such as mine, came with a riveted coupling. When it wears out, you throw it out.
You need to change the coupling only if there is some undue "play" in it; if there is little to no play, put it all back together as the problem you may be trying to solve lay elsewhere, such as your steering box.
If you need to replace the coupling, it should not be too hard to find. I think MB still sells it. Check the Classic Center.