It will fit in the 767 without a problem. Remember your connecting flight in Bucharest means you don't have as much space. Why not take one of those dog purse thingies?
20cm x whatever, seems such a small space for any animal on a long flight, surely they must be some laws about this?
Hahhahaha, they don't exactly care much for the big animals sitting in the seats, what makes you think they care about the small ones under them?