This is a 1934 Briggs & Stratton Model Y ½ horsepower gasoline engine. These were mainly used for running washing machines, but variants were marketed for landscaping equipment like lawn mowers, roto-tillers, and such. Briggs made the Model Y from 1931 until 1940.
The seller’s grandfather told him it ran when he put it away 40-odd years ago. Hey, if you can’t believe Grandpa, who can you believe?