the above download contains 4 different cars. Each car has an extension folder. Inside the extension folder are an ext_config.ini and a folder data override. The display lua doesn't go into the lua app folder bro!!! The whole extension folder goes into the car folder inside content. Klick "ok" when prompting to override.Yes we are talking about the extension folder.
After that it depends if you want to use the buttons in Content Manager, Patch, or the override method with the file in the extension folder.