Sorry to say this, however I very much doubt that you will be able to ride through China. Riding through or into China is just about impossible. I've enquired along with many others, China doesn't seem to want tourists with their own vehicles.
There are tours which start in China and ride out, but none that I know of which ride in or through. Try doing a search on this site, there is a lot of links.
If you find a way to do it let me know and I'll ride through in August when we are riding from London to Vladivostok, then Japan. We are returning to Hong Kong to live however can't get there through China.
Good luck with your trip, all the same. It sounds great.