John, I just got through the same procedure on my car. I decided to replace all of the old universal joints while I was at it (the boredom of a long canadian winter I guess). The clips do have holes for snap ring pliers. I got mine and the gasket from the local GM dealer here in town. It took only 10 seconds to install the clip but took many hours to coax the differential out of its home. The rear crossmember will be a challenge to remove if it has never been out of the car. I bent a 3 foot pry bar trying to pry the crossmember of its cushions mounts. It took a 5 foot bar to do the trick. Make sure you support the differential carrier before prying as it weighs about 45 pounds.
The shock mounts can be rusted pretty good. If you need to remove them make sure you get a shock mount removal tool. I had to beat on mine for an hour before they finally broke loose and no damage to the thread. Best of luck....Mark