Older one: Leviton 5320-I
Newer one: Leviton 5320-W.
Same basic model. The I is for ivory and the W is for white.
The older ivory one is made out of bakelite and would have round plaster ears. Hard to tell by the face, but I think the design dates to the late 60s. The only change that I know of during that time was that the ground screw moved from facing down to facing the side.
The newer white one would have been made after an approximately 1995 redesign, where the bakelite was replaced with thermoplastic and the plaster ears are a larger square shape. The thermoplastic faces have a little molding lip visible around the perimeter of the outlet face. They're basically unchanged today.