This is actually quite a different request to the original (it is the opposite sort of flow), so do think in future about posting a new topic. You can alway include a link back to any related topics.
You would have to import each file effectively creating a snapshot of the files in Drafts - Drafts does not work directly with files in the file system.
You could use wiki style cross-linking to link from your index draft to each Scratchpad file draft. But you could also just have a workspace that you use to review the Scratchpad entries and use the draft list as you index draft. If the index is never to be manually modified with additional content then I would go the workspace route.
You might also want to archive prior Scratchpad drafts as part of your import process just to keep everything current and clean.
You would need a (Java)script-based action to do this, or you could use Shortcuts to build everything in Drafts)and you can even call that from an action in Drafts with a non-scripting step. Shortcuts is easier to get started with, but if you have programming experience (depending upon the language), JavaScript might well appeal. I would suggest spending a few hours learning a bit of both and then decide on your tool of choice. If you get stuck, then we can all pitch in and help.
Hope that helps.