Even considering going back to a 40+ year-old design is an admission of failure - pretty typical for government funded projects, when compared to the private sector.
The 747 is still being made, 43 years after its first flight in 1969, the year of the first Moon rocket. The 737 is still being made, first flight, 1967. Sure, they're different now, but the fundamental design is still there. They're still competitive with much newer designs, otherwise they wouldn't be offered anymore.
I'm not sure where the DC-3 comparison comes in, is there a new regime of rocket engine that compares with going from rotary piston prop to jet engine? Even SpaceX's home-built Merlin engine isn't some fancy design that supersedes all engines before it, at least not in the manner from piston to jet.
I'm not sure where the leap from 40 years difference and 60 years in your comment.