The repair couldn't have been more simple.
First, for the Endcap, I removed 2 screws to take off the drawer slide on our old part, and 2 more to remove the broken Endcap from the fridge wall. Next, I put the old drawer slide on the new Endcap by replacing the screws. I then slid the Endcap in and replaced the screws which hold it in place. Done!
For for the center rail, I simple inserted the tabs on the replacement part into the slots in the fridge. Done!