So, as some of you may know, I just purchased and cleaned up a new
rear end(pictures coming soon) for my '79 210. While my friend and I
were working on it, we noticed one of the swing arm brackets was bent
slightly. In an effort to bend it back, my friend stuck a socket
wrench handle through the hole and put a jack handle over it to create
leverage. As you may have guessed, the bracket bent back into place
but now i'm left with a warped hole. Part of the hole now protrudes
into the inner part of the bracket and the swing arm will no longer
slide all the way in. We tried using a vice to flatten it out, but
that bent the handle. It's so frustrating to have this not work, this
is the last thing I need to fix to get it back on the road. Any
suggestions?

Try a "C" clamp to flatten the raised area.

Another thought... two sockets back to back to sandwich the bent ear. Couple of large heavy duty washers on both sides, then a bolt and nut to tighten down. Large washer keeps the nut and bolt where you can reach them, sockets flatten the bent ear.

you may not want to keep bending this thing... post a pic - i think i have spares laying around.

you'll need to supply bushings...