Paul,
Thanks for chiming in - yea, I googled 'images' and started to see why it won't just swap in. Darn. But then again, I'm not trying to make a boy racer out this car (which is why I bought a Merc instead of another beloved e30 Bimmer) but always relish the chance to make an improvement when I have to make a repair. The car's not in perfect tune, true enough, but far worse is the stupid 4speed slushbox cabled to an awkwardly highly geared rear end! I know the Europeans love to rev their motors compared to us, but this is absurd! No tach of course but I'm SURE I'm pushing 4K at a hair above 70, and at 80 I bet bottom dollar I'm over 4K. Maybe fix exhaust as I described above and swap rear ends? Or drop the running gear from my w124 230te (still held hostage in Montreal, btw!) into my w123 and really have the car I want (or pony up the dough and buy this one!)

Mercedes Benz 300 Series 300D | eBay