Do a full back up of your current forum. Then upgrade it normally so that you have a 3.8.2 site working. Then do another backup
do a clean install of the new file on another file location like a test site.
then after you have it all done and set up with just the one forum on it and you as admin, go ahead and do an upload of your database through phpmy admin or any of the other proven methods to restore a database.
This will give you the same you will have on the main forum minus al hacks and style themes
After you make sure everything works then move the test site to your domain and delete the other one
Done
Done that. Although I still see the hacks and plugins still there. Well, since it was the same DB which I restored from. Any method to only restore users, posts, threads, attachments?