setting default permissions

We have a RHEL 3 scp/sftp server. This server houses several
department subdirectories. I would like any new files/directories
under a certain directory to take on the group ownership of the parent
directory they are placed in, and also have 775 as the permissions. I
have executed a chmod g+s to always have the group match the group that
owns the parent directory. However, how can I have the permissions set
to 775 (or at least 665). I don't know/think that a umask will help as
the user is not doing this from shell, but copying the files or
creating folders via scp/sftp client. Anyone have a solution? thanks
in advance!!

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