Go to x64e, the author has already modded those files so they appear as mods: x64e and so forth because its under his mods if you get what i mean, so for you again just ignore the mods and follow the directory. Once you have placed all the files like instructed they will appear for you as (mods/x64e/levels)
Example: the authors view (mods/x64e/levels/gta5/vehicles/airbus.ytd) Your view (x64e/levels/gta5/vehicles/airbus.ytd)