Finally it's here!

How to play with Steam current mod? Easy and Fast. Steps.

1) You needed bought game in Steam first of all for sure.

2) Next part is on screenshot: 

Go to properties in your game(remind: it must be bought).

3)Select path to the game (if game is bought and FCAV already installed via Launcher, - you can choose custom Far Cry 1 folder also):

"D:\SteamLibrary\steamapps\common\FarCry\OpenFC\FarCry.exe" -MOD:FCAV %command%

As you can notice here, path is on disk D, is just EXAMPLE, your path may be different, so find where is your bought steam game is located, and select there FarCry.exe from OpenFC(this folder will appears in your game root folder ONLY when you will install the mod - via launcher or manually).
UPD: Also all screenshots etc will works for Steam Community content. It can be uploaded there.

After that your Steam Overlay will works with FCAV. Enjoy!

Download FCAV mod here: https://farcry1.itch.io/far-cry-advanced-version#download