Here is the other two toward the top of the rear face of the block. The one on the right is directly into the passenger lifter galley. The one on the left is just a "clearance/access" plug to access the one for the left (driver's side) lifter galley:
Here is a closer up view. I have seen recommendations to drill a .060" hole in this plug to help oil the distributor drive gear you may or may not choose to do that: