92 3EE : What's the ball behind the oil pump?

I am overhauling a 1992 3EE engine. Behind the oil pump is a ball inside a hole. What is the function of this? Is this related to the pressure regulator or anti-drainback? Are there any service specs related to this? Any suggestions would be appreciated.

Love to answer my own posts. It appears that the ball behind the oil pump is intended as a plug, although why this is used rather than a cup plug, as at the rear of the block for this same longitudinal oil rifiling, is unclear. Just wanted to make sure the ball isn't some spring-loaded & seized component.