Length? The 773 is longer than a 747. The 773 also has 5 exit doors (the extra being an overwing missing on the 772) on each side.

Did Boeing keep any 777s for demos or R&D (other than the one deliberately destroyed in static testing)? FWIW, the first A340-600 cannot be sold for pax use as it only has 4 pairs of exits (how Airbus wanted to sell it) and the J.A.A. ruled that the distance between exits was too far.