Here is the entire package ready for play! It is released as is.
For Windows: Browse to C:\Program Files (x86)\Steam\steamapps\common\Portal 2
For OSX: Browse to ~/Library/Application Support/Steam/SteamApps/common/portal 2/
Next rename “update” to “update.old”. Next place the extracted “portal2_dlc3” and “update” folders into this same location. To verify they should be in the same place as “portal2_dlc2” and “portal2_dlc1”
To revert back to playing Portal 2, rename the “update” folder to “update.wibi” and rename “update.old” back to “update”. Then rename “portal2_dlc3″ to “portal2_dlc3.wibi”. You can repeat this as necessary to switch back and forth.
Once installed, make sure Steam is running and Portal 2 is fully updated, then either double click on the desktop icon if you used the installer or launch Portal2 as normal if you used the .zip