Your install is on your G: drive and Steam is on C:?
If you want to recover your old steam library, if it still exists, then I suggest you find it (usually under \program files (x86) on your original C: drive)
Then:
Exit Steam
Delete all of the files and folders except the SteamApps folder and Steam.exe
Run Steam.exe in the recovered directory, make a shortcut to this for future use and/or update the existing shortcut.
Steam will then re-download itself, and recover the installed files (they will need to re-install but not download again)
The My Dovcuments folder you mentioned, copy contents of that to your new one after running IL2 BoS once (so it creates a new one).