Adding a note to a 7th chord makes the chord an extended 7th chord. I define a double extended chord as two scale degrees added to a 7th chord. There are 3 dominant 7th extended chords that can be built from the major scale: 9/11, 9/13, and 11/13. I have 12 open guitar chord voicings for those chords in G from the C major scale.
every open and closed guitar chord in standard tuning
All chords are available as PDF files