Please see Discourse Migration - Literate Computing
There isn’t an existing import script for FUDforum, so a new script will need to be developed, which might make your time line a challenge. I’ve done over a hundred migrations over the past 9 years and have done many custom migrations. At least one I did in under a week.
If you’ve got an mbox file(s) then it should be pretty easy. It’ll be more work to not import the users, but there are ways to do that.