There is an Import button at the bottom of the menu (left side), you can import (old) .8bf plugins into an existing database or one that you created.
Once in the database, select the database button next to the import button, and select the name of the database you wish to use, ie Photos.db, the photos plugins should appear in the filters menu.
Most, not all .8bf plugins work on Filters Unlimited.
You may find some plugins that are already setup for Filters unlimited, these files are .ffx files these can be added directly inside the Filters unlimited Folder, in one of the database Folders. (Database Folders names end in .db)
Below are a few example names of Filters Unlimited Plugin Database Folder and filter Files that can be found in the Filters Unlimited Plugin Folder. You can create your own database for each plugin. Inside these folders you will find the .FFX files these are pre- imported Filters Unlimited plugins. (One folder per plugin, ie all Background plugin files are in Background.db folder).
Example plugins (inside database folders)
__Background_ – _Smoke.ffx
__Background_ – _Splash.ffx
__Background_ – _Swirl.ffx
I hope that Helps