Help with Door Glass Track Installation

I have a 1970 Duster which was missing the door window rear track when I bought it. I have procured an NOS part from Ebay but I have no idea how it is supposed to be installed in the door. There is a threaded bung, or, nut at the top but I do not know how a bolt is supposed to go in there. I have uploaded a picture of the part in question just in case my description is inadequate ( which is often).

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