I ordered a new unit yesterday. Looking at some pictures of the new unit and referring to some youtube videos for installation, I believe the rivets are just to hold the tabs in place. It seems, from pics and videos, there are tabs that are bent out during the install. There are then corner braces installed for maybe support. The unit is actually screwed in place from inside the box. You can see these screws in the pictures I have attached.
Once I receive the new unit, I will start demo part of the original unit. I will learn more then but I was trying to gather as much information as possible prior to the demo.
If you see or know of anything that I should be aware of or watch for, I would appreciate any input.
Thanks for your assistance