If ya wanna know something you didn't know about Cox engines here is a good place to start:
http://en.wikipedia.org/wiki/Cox_Model_Engines

This was my first experience with this page and While it does not have every known detail of these engines it is a good place to start. Or as a reference to certain details or data. like how many different heads are there for the 049/051? Or how can you tell which cylinder is which and how does the porting make a difference?

Lots of pictures and data to read over and of course links to other details like "1/2 A class" which leads you to a chart of Model engine classes.

Robert

another site that is great if you don't already know about it

http://www.mh-aerotools.de/airfoils/cox_frameset.htm