[]>When doing the import there is no way we'll be able to keep the post #'s the same.

How about keeping a conversion log in a mysq ltable that has 2 rows, old post number, new post number, and then use those data to feed the 404 error redirection script? [/]

That might very well be possible. I'll be modifying the current .classic -> .threads importer to work with the new database design and should be able to do that without slowing things down too much, will take a look when I get to that step.