That is a jack handle for a Model T. You need to choose your friends more carefully...
Just kidding.
That is the front track. Picture #2 shows the folded over clip which grabs the bottom end of the glass channel.
You are going to have fun reattaching that back into place. One thing that you will have going for you is that the metal fatigued, broke off, and left the corners spot welded to the inside of the inner door sheet metal. This will allow you to find exactly where it goes.
You will need to completely gut the door of most parts which will come off. You should be able to see the 4 spotweld marks on the inner door sheet metal.
I would drill pilot holes for 2 self tapping screws between the pair of spotweld marks for the top and the bottom flanges of the part. Then you can use the the sheet metal screws to hold the part in place so that you can drill four 1/4" holes through the door panel and weld the part to the door panel from the outside of the door.
Working on doors doesn't get much more fun then this.
Carl

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission