Sorry SHJ and Panop, but you are both incorrect regarding your sighting of Pakistan Air Force Connies at Northolt as the PAF never operated them! It was PIA that had them and flew into LHR during the '60s and may possibly have taken one into NHT.
Fair enough - on reflection I'm not sure what the Pakistan AF aircraft that visited Northolt in the early 70s were. Can anyone remember?
I do recall a PIA Super Connie at LHR around 1967 or so - it was parked up for a while at BOAC Maintenance if my grey matter recalls correctly.