335s and 290mm identification

This may be very basic, but as a newcomer I am trying to learn the differences between some of the mid-1050's racing cars. I seem to come across a wide range of photos of the 335S and 290MM cars that make them appear quite similar. And then I find that some of these cars began as 860s or other models. Other than displacment and engine configuration, how can I easily identify these cars from that era? Thanks.