An actual Catalina I or PBY-5 would basically be a new plane due to changes to exterior model, as well as many minor changes to crew stations. Canso-A/Catalina IV, PBY-5A, or PBY-6A would require changes to the game engine to allow amphibious aircraft.
How come the last three you mention would require changes to the game engines? Has that to do with the ability to land both on water and on land?