There is a bracket that spot welds to the cowl on the inside, see the pic.
https://www.flickr.com/photos/advance-design_parts_co/8129104279/in/album-72157631867396207/
If this has been broken loose while not attached to the vent it will drop into the fender. You could fabricate a bracket but short of welding it back in I don’t think adhesives will work due to the leverage/force applied to it. As far as I know the bracket is not reproduced, broken off, missing brackets are common as it is only held by pressure and two spot welds.
https://www.flickr.com/photos/advance-design_parts_co/12647382934/in/album-72157641244124604/
The 2 screw heads you see in this view belong to about 1/2” long bolts that go through the bracket above.
Here is the entire assembly (early ‘49) showing the 4 Stove bolts and all the parts. Yours may not look exactly like this as there are 4-5 different hardware versions depending on year.
https://www.flickr.com/photos/advance-design_parts_co/8129342725/in/album-72157631868452754/

1950 Chevrolet 3/4-Ton 3600
More pictures on Flickr