Actually, in the very beginning of the 4 Crown they ran the old USAC Stock Car division along with the midgets, sprints & Silver Crown. The USAC Stock Cars were part of the 4 Crown in 1981. '82 & 83. At that point USAC dropped the stock car division and replaced it with the dirt late models which was part of the 4 Crown until 1995. 1996 was the first year for UMP modifieds as part of the 4 Crown.
Here's what the stock cars looked like at the 4 Crown in 1983.
https://www.youtube.com/watch?v=BCOEx9086aY