Dude,
You're missing your pins.
I'll see if I can get a pic of one if someone doesn't beat me to it.
The center or each pin goes in that hole and both side touch each other in the middle.
He was a Chevy guy wasn't he?
EDIT: My pins and extra pig aren't here at my house, so no pics.
Here is a pic that I drew in paint, to try to give you an idea of what you should see there. The pins allow you to push the right axle into the other to adjust your bearing preload. The pushing pin should not bottom out in the center section before it seats the driver's side axle bearing. These go into the hole that are in your pic. If you want to put it together tonight, you'll have to cut a bolt like I suggested up above.