Do not use 747's for long haul. The maintenance will eat up your profits. In the late 60's you can use DC-8, Boeing 707 or Ilyushin Il-62.
For the Caravelle, you can consider the DC-9 series, wait for the 737, try the British Hawkes Siddeley HS121 Trident or go for the excellent Tupolev 134. Otherwise just replace with new Caravelles.
I hope this helped
