Thanks guys for your comments
Concerning the carbon tank, it comes from Franck Carbone :
http://www.franckcarbone.com/rayon.asp?id=401
This guy made the carbon parts for the SIMA limited edition of the M900
Mine is probably the last one that has been made
(Parts to built it are now missing).
The look and feel is very qualitative.
What is also nice about this tank, compared to the original one, is the gain of weight. That makes the motorbike much more better to drive