I just posted my final scripts as a gist. I honestly don’t remember what I did there, or how specific that is to my community. But maybe you can diff those scripts to the originals and see a few problems I solved, and things I added. I tried to make the import more complete, I hate losing information in migrations.
→ importing-from-kunena-3-to-discourse · GitHub
and
→ importing-from-kunena-3-to-discourse-2 · GitHub
I hope this helps.
EDIT: I just remembered I used a mixture of Ruby scripts and SQL commands (I recommend DBWeaver for a practical SQL console during migrations). I can post SQL fragments if there is interest.