Just a quick update on this thread: I was able to procure a full set of five pressed alloy 123 rims (6") so I went ahead with the 205/70R14 Michelin Defenders. It took a while to have the wheels stripped, powder coated, and mounted with tyres, but they're not yet on the car. I'll report back once I've driven the car a bit.
I read through most of the reviews, but it can be hard to decide based on just reviews. Firstly, reviewers don't always indicate the make/model of the car and the corresponding tyre size they're basing their review on. I had a detailed discussion with a local tyre shop manager, and he mentioned different tyre dimensions can play a big role in how a particular brand/model tyre performs, and it's not easy to translate that to our particular size (e.g. sidewall stiffness is dependent on the tyre profile dimensions being considered). Secondly, the particular car type and how it tends to be driven sets the expectations on tyre performance. I finally came across a number of mentions of the Michelin Defender on some generic MB user forums that specifically talked about installing 205/70R14 on their older cars (w108/w111/w107 etc), and they were generally all positive, so I took the plunge.