The following text from Aviation Week is not unique to the aircraft pictured:
02/03/1964. Aero Spacelines, Inc., has obtained options to purchase
two English-built Saunders-Roe Princess Flying boats from the
still-unidentified European company which recently bought the three
existing Princesses from the British govenment. Aero Spacelines
plans to submit an unsolicited proposal to NASA to convert the
flying boats into turbofan, land-based aircraft to haul Saturn
rocket stages. View also photo 44 and 10571.