Bucket seat hardware???

I have a '70 Dart Swinger 340 with bucket seats. My issue is that the seat backs have no hardware to keep them attached at their top end. There's two holes, but that's it! I recently purchased a package containing over a hundred interior screws, but nothing is marked for this location. :banghead:
Does anyone know what is correct and where I can acquire it? Your assistance with this matter is greatly appreciated. :prayer: