Xenforo is going to be releasing the IPS4 importer shortly and we'll need a redirect script. I've helped them test the current beta importer, but I can't go live with the conversion until a redirect script is released. I did preserve all of my content IDs, so I'm told this wouldn't be a difficult task.
I'm not real familiar with the inner workings of the URLs, but if you need me to provide something, just let me know. I know at some point, someone is going to make this script just as all of the other scripts have been published.
We'd need example "before and after" URLs to make any recommendations. If the URL format hasn't changed though, the IPB 3 redirect scripts would work (though if you maintain IDs, you generally don't need scripts, just .htaccess changes).