The P6-E is a biplane so I don't think finding the CG is quite that easy. There's a large thread on this plane in the Warbird section I belive. They should be able to answer your questions there. Do a search for P6-E.
http://www.rcuniverse.com/forum/fb.a...831&key=P6%2DE
Never mind the search, just click on this link.