What's to be confused about.
It's a GM truck pan for 4x4 trucks with center drain vs side drain
https://www.summitracing.com/parts/rnb-264-132?seid=srese1&gclid=CjwKCAjw5MOlBhBTEiwAAJ8e1ga2eWSlhIyrnfEiGh7EBzNWZhvxHz4zzjsmlPeD4DuLbAC-9iASjBoCR3UQAvD_BwE
The adapter is screwed into the drain plug