The engines in these cars corresponds to the name. The 230, 250, and 280 all got straight 6 engines, while the 200, 220, 240, and some 230 models were sold with either an I4 or I5 engine.
Some of these cars featured a 5 cylinder diesel engine - the first like it in the world in a production car. Although this was a time before Mercedes became obcessed with competing with and beating the likes of BMW and Audi, some of these cars did sport some rather impressive performance figures. The 280 in particular outperformed just about anything of the day.
Along with the non-descript numbers that were the names of these cars, they were also often followed by a trailing letter to describe the body type. For most that would be an E, which denotes a saloon car. A "C" was added to this E to designate the coupe models. The 280CE, for instance, was a coupe model of the 280.
The stroke 8 is often the name used by car enthusiasts to describe this generation of cars from Mercedes, although it was never a part of official designation.
These cars are out there on the used car market, if you know where to look. In good condition and from the right year with the right options these cars are collectors items. You can find them listed on eBay, along with plenty of rare or obscure parts.