I don't mean copy and paste each thread, I mean you;
- Compare the differences between the PHP Fusion db and the MyBB db - Apply the differences, i.e. maybe PHP fusions posts column is 'pf_post_content' and your MyBB one is 'mybb_post_content' or whatever it may be. - Run the query and bobs your uncle
Obviously its easier said than done, but it's better than looking for something that will never exist. Especially if you haven't got anywhere in 2 years!