For the flashback to "Too Hop to Handle", the setting was changed from a country house to a city apartment. The background is actually recycled from The Honey-Mousers (1956).
In the circus flashback, Tweety is actually shown flying, a rarity for him.
The flashback to Sylvester's childhood is actually a scene of Sylvester and his own son.
Classic mid century Hollywood style architecture for the animal clinic, as is common with this era of animation.