The 747SP ... <snip as irrelevant> ... even completed a 54 hour flight
Not exactly so.
To celebrate the 50th anniversary of Pan Am, flight 50 as it was called flew a
route from and to San Francisco that indeed took 54 hours, 7 minutes, and 12 seconds to complete but it was actually comprised of multiple sectors. Stopovers were at London Heathrow, Cape Town International, and Auckland Airports.