In most cars the seat is upholstered and then installed. In the coupe that is true for the seat bottom but not the back.
The back is about three-quarters upholstered and then installed. Final upholstery happens in the car. That includes the accordion strip that attaches to the package tray...and I seem to remember some fabric "loops" that hold the spring set to the car.
Here is a link to a thread that I contributed to some years ago. In that I described how to remove the seat, which may help you envision how to put it back in.
https://www.fordbarn.com/forum/showthread.php?t=115366
Ken