Abbottgod

I have searched diagrams all over and still can not figure out the name of this piece. What is it's exact function and where might it be possible to find a replacement?

It never made a noise before. I had came 50 miles driving home and yes the last 3 miles I drove at 25 mph it made a slight clunk. Not very loud. Then what I described happened on that last 3 miles. Do you think I need just new bearings?

My rear end lost power all of a sudden. The transmission would spin freely in any gear but no power to the rear end. When i would shift it back to park it made a grinding sound. I had a friend come try to pull me home with a strap and the passenger side tire came off with a rod attached. I called a flat bed tow truck and have it home now. My question is from looking at the pictures do I need a whole new rear end? Can this one be salvaged? And any ideas on what exactly happened? Thankyou in advance and it is a 1975 buick regal with a 350.