Yes, don't do it.
Try using TinyPortal instead. The last time I attempted a joomla bridge, I spent 2 days rebuilding my whole SMF site.
Your best bet is to set up a completely seperate instance of SMF and Joomla, get them working exactly as you want and then import your database into SMF. Then repoint your traffic to the alternate url. Ideally, if you time it right, you will only lose a few posts from the time you import the database to the time you repoint.