It depends on the speed rating which in turn depends on how fast you want to drive your car, even occasionally. Originally that car came with 185/82-VR14 tires. The closest to that is 195/75-14 but I don't know of any being V rated or even H rated. You can find them with a white strip.
A popular replacement size is 205/70-14 and you can still find them H rated, good for 210 km/h. You can get then V rated if you buy some classic XWX Michelins (a very common choice for that car back in the days) or Vrederstein but they're expensive. No white strips.
Personally I believe the 3.5 Coupes and their low front grill are better with biffier 205/70-14 black walls which was a replacement size officially recommended by Mercedes. H rated is enough for most applications (if not all). Then you have a choice between cheaper modern design or more expensive classic design.
BenzWorld.org forum is one of the largest Mercedes-Benz owner websites offering the most comprehensive collection of Mercedes-Benz information anywhere in the world. The site includes MB Forums, News, Galleries, Publications, Classifieds, Events and much more!