The maps in the Chassain guide, though old are excellent. If you can read maps, you don't need the words.
In 2010 the waymarking was mostly good except for one section of about 5 days when it was non-existent.
The Chassain route is not the same as the GR route, it is more direct.
You need the guide to tell you where there are shops and accomodation. Not all villages have shops.
Send me a PM with your email address and I'll send you my itinerary.