Have fond memories of visiting LHR - Hatton Cross, on a number of occasions in late '60's whilst working for RCA Aviation Div at Sunbury on Thames. Particularly when Pan-Am flew their very first just-delivered 747 there for an inspection by interested parties - which included me, in July 1969 or thereabouts. First impressions and comments were "They must have assembled it in a hangar as it couldn't possibly have flown here". Photos in AW&ST came no where near in conveying the immense size of the beast. Heck the 707 was king back then.