Pan Am B747SP's were kind of rare to see at Miami International Airport due to other routes they were needed on. I believe this aircraft was being ferried to their new owners at United Airlines, possibly via New York-JFK, who bought Pan Am's Pacific routes and certain aircraft types so that Pan Am could stay alive financially.
Ironically, in the first part of 1981, I flew on this aircraft non-stop from Los Angeles to Auckland, New Zealand for most of a week on both the North and South Islands. After almost a week I returned on this same aircraft flying non-stop from Auckland to Sydney, Australia and then non-stop from Sydney back to Los Angeles. It was approximately 15 hours on the long legs but only number two or three in length for Pan Am routes.
This fine B747SP carried the "Flight 50" emblem because it was flown to celebrate Pan Am's 50th Anniversary on a flight from San Francisco to San Francisco over both the North Pole and the South Pole with stops at London-Heathrow, Cape Town, and Auckland, New Zealand. The clipper name "New Horizons" was formerly the "Clipper Liberty Bell." Captain Walter H. Mullikin commanded the 54 hours, 7 minute and 12 second flight creating seven new world FAI-certified records.