The first item to go back into the block is the oil distributor.
You can see in the photo below the two holes in the block where it mounts.
In the exploded view of the parts, there are a couple of things to notice. Under the spring-loaded valve, there was a gasket that came out in pieces. I couldn't find a washer the same size (1/2 ID x 5/8 OD), so I made one out of a flattened piece of copper.
In the oil-on-the-towel-circle, there is a small curlyque of hard plastic that was caught in the spring valve. I have no idea what it is or where it came from.
In the bottom photo, I am starting to put the oil distributor into the block. Notice the hole on the side of the oil distributor body. This hole squirts oil into the oil reservoir for the center main bearing.