When Mary Ellen was reading the book Gone With the Wind, Dr. Spencer compares her beauty to Scarlett O'Hara. The book specifically mentions that Scarlett was not beautiful.
The preview scene that runs before the opening credits isn't in the actual episode.
At 13:25, Grandpa mentions loblolly seedlings. Loblolly pine is one of several pines native to the Southeastern United States, and is the second-most common species of tree in the United States, after red maple.
The comics page Grandpa is seen reading at 21:35 is a standard prop newspaper used in TV shows at the time; none of the comic strips on the page are real. The same prop newspaper can be seen in the 1952 episode of Mr. & Mrs. North (1952), "Comic Strip Tease."
Whilst waiting for a slow elevator with David, Mary Ellen comments, "It's certainly not the Dixie Flyer." The Dixie Flyer was a premier named passenger train that operated from 1892 to 1965 via the "Dixie Route" from Chicago and St. Louis via Evansville, Nashville, and Atlanta to Florida.