I remember an Illinois Central wooden caboose that IC ran between Hopkinsville KY and Nashville TN. This was the old Tennessee Central West Division that IC took over in 1968. I saw it between 1969 and 1974 or so. It looked like a converted box car because it did not have a cupola or bay windows. It did have a small sliding door on each side to allow the conductor to reach out and grab train orders without having to stand on the back platform. They believed this practice was safer.
Used to see those all the time during the '60s on the local that delivered lumber to the neighborhood lumber yard.