I still can't figure out what is missing.
If you're using the original wiper, the original refill is held by the raised section. Here's a picture of a 1970 on FABO
[img]https://www.forabodiesonly.com/mopar/attachments/dscn0867-jpg.1714700597/[/img]

If you're using a different style refill with a spring clip on the end(picture linked in my earlier post), the spring clips come with new ones. The correct refill length is 15".