A while back, we were requested to create a backup of a facebook group. It was a very simple task, so to manage it within 5 minutes, JS developer wrote the ripper in NodeJS and at the same time simple Python / Mako script for templating json was written.
You can find instructions in Readmes. Basically nodejs script rips the group into json and python script is a simple parser that creates simple html from json.
Please note, that there is currently ( 2014-01-04) a bug in facebook API, so some of the attached materials to the group posts may show up as "Unavailable" in backup.