You can only be valid on one type at any given time with the Chinese. If you are currently flying the Airbus, then in all likelihood that is the fleet you will be hired on regardless of your past 777 experience or vice versa. You will be hired as the second Captain which means that you will operate whatever sector the PIC dictates - but then the sector is, for all intents and purposes, yours. They rarely (if ever) intervene as it's a matter of face and they would not want it reciprocated. The only carrier I know that hires 330 Captains as PIC is Air China - there may be others but not China Eastern (I should know).