This is an article I wrote on a different website over six years ago. With that website now shut I have added a few highly viewed posts to Tweaked for your Pleasure.
If you have ever converted over to bbPress or have a bbPress forum and decide to add a
WordPress installation over which has users already stored in it that you will know when you come to actually integrate the two that bbPress will show all the posts has the wrong users.
This is due to different IDs within the WordPress database. I had this problem with Just a Community and Tweaked for your Pleasure. I got around this problem why writing a tiny script. This script assumes all the users exist on both side (there are plugins to import bbPress users to WordPress) and if not, it will just put it as Anonymous. You will need to mod the script yourself but most of it is done for you already and yes, it is very badly coded.
It also assumes you use two different databases. Just edit were needed.