There are two ways to install this pack, but the is highly recommended for a file this large to prevent errors. Manual Method (Recommended):
Do not use the stock Assetto Corsa launcher. Content Manager is mandatory for managing large mod packs. pack 1447.rar
Since the file is a .rar archive, you need a modern extractor to handle the compression. There are two ways to install this pack,
Inside the archive, you will typically see folders named content . pack 1447.rar