Fill plug is on the driver's side front of the diff...above the support rib
As for the C-clips Remove the cover and spin the gears til you see the bolt that holds the pin in. I beleive it's removed with a 10mm wrench. Remove it. You'll notice the crosspin will now slide in and out. Push it in about 1/2 and spin the gear 180degrees to the other side and remove it.
When the pin is out, DO NOT rotate the axle shafts unless you spin both together. If you turn one, you run the risk of the spider gears falling out.
Push 1 axle in at a time. Look inside where the crosspin was and you'll see the c-clip on the end. A magnet or long needlenose pliers makes removing it easy.
Installation is the opposite of removal.
It's a pretty easy job, but i suggest a shop manual if you are hesitant.