As an aside, I often wonder why Lockheed didn't do a study into offering the C-5 as a commercial freighter. Volume wise it would be a better proposition than the C-17, although still inferior to the 747 which utilises its interior space more effectively with the dual decks.
The Antonovs have shown some need for a low-floor heavylifter outside the old Soviet market, and there hasn't really been anything except the Hercules in recent years. The greater internal volume of a C-5 together with its high payload might have supported a small fleet in the civil sector, if re-engined to the CF6 commercial versions.