You might start here. There are sections on the different classes with some plate drawings. Nothing too deep, but it's a start.
http://home.cogeco.ca/~gchalcraft/sm/
Next, depending on how detailed you want to get, this is probably one of the best sources.
http://www.ospreypublishing.com/stor..._9781846030079
There are probably others out there, but Osprey has a good reputation and includes colour plates.