Many of the previous "full packages" provide modified versions of the necessary files, such as product_info.php. Unfortunately, I have no idea what versions were used as a base. Looking at the headers, it looks like something from 2003. These files are missing some important security fixes, and are probably not advisable to use in my opinion. I have taken the v2.0j and the advanced search fix below, and created a .patch file that contains only the PEF changes. This can be applied to a current version (i.e. rc2a), so that you get the security and feature benefits of having up to date base files as well as PEF. Those on a linux system can simply start with a vanilla, up-to-date osCommerce installation, place this file in their catalog directory, and issue the commands

gunzip pef.patch.gz
patch -p1