The one closest to the mounting bracket is suppose to have a plug in it. The one farther back is for your oil pressure sensor. They are both along the same galley line, I do not know why the front hole is in there, manufacture, or perhaps turbo options in other models. Sorry I also do not know the thread pitch to plug it up.
Here is a crappy picture of my block on the way to get tanked. you can see the plug right in the center of the four mounting bracket bolts that are on the right of this picture. You can see that the hole to the left (Under the oil filter) is open, that is where the pressure sensor goes.
hope that helps.
