Where does the radio strap connect on the body?

I was expecting to see a stud somewhere under the dash, but couldn't find a thing. I ended up fabbing an extension from the defroster vent mount, which is going to work, but I was wondering what Chevrolet did from the factory.

Do you mean the bracket/strap that supports the end of the radio?

If so, it attaches to the passenger side of the radio housing and goes down to the dash support brace that runs between the radio and ash tray area. If I remember correctly, it attaches with a sheetmetal screw going into one of those U-shaped "speed nuts".