You can't migrate posts that are more than 60 days old... Judging by this query that means that 98.2% of all (undeleted) questions tagged code-golf on Stack Overflow are ineligible for migration.
Of the 4 that are eligible for migration 3 had nothing to do with golfing (1, 2, 3) so I've removed the tag. This means that there's 1 question, which might be on-topic (I'm not 100%) and it's asking for help rather than posing a challenge.
If you're serious about migrating questions from Stack Overflow you'll need to be organised. Have a feed of all questions tagged code-golf; remove the tag, if it's not applicable and flag using the "other" option if you want it migrated. You have to do this before it gets downvoted and deleted, which can be extremely quick (not that I have any idea of the proportion of questions that this happens to with this tag.)
To be honest, I'd be quite surprised if you got many good new questions out of Stack Overflow...