You would not import anything. You would simply upgrade your forum reviewpost and classifieds to the latest.
If your trying to install a clean forum and want to reinstall/move your reviewpost classifieds to that forum your going to have issues since no users exist on that new forum therefore you really if your installing fresh install everything fresh.
I guess I dont really understand why your talking about a clean install when all you need to do is upgrade. If your trying to transfer everything to a new site and discontinue the old site then thats what you would do which means moving all the data not starting fresh.