Like mentioned earlier this is a plug that covers where the
oil galley comes up from the passenger side main
oil galley and the lifter galley are drilled and connect to the drivers side lifter galley. These are not removed most of the time during a rebuild and they should be to clean the
oil galleys good. They have a tendency to come out after replacing so will drill across the top and pin them. You could also peen around the top mof the plug to help keep it from coming out. If it is still in there just re-install the intake because it should be there. Good luck, Keith