I flew on a BA 747 ‘Classic’ in 1978 - on an APEX fare so no sniff of UD if it was Y then. Paper tickets MrD and I checked in at Victoria (old BOAC) and were bussed to LHR.
We had joined BA’s ‘Friends and Families Overseas’ club and were surprised to be paged in the departure lounge (T3) by a representative giving us hints and tips for our journey to ORD as well as the US in general.
Seats were allocated at check in from a sticker seat map- your allocated/requested seat would be affixed to your BP. I remember having 2 catering jars of Branston Pickle in my hand luggage, not something you could do now.
I also remember flying on a Tri-Star from LHR - AMS in the late 70s or early 80s which was the only time I ever flew one.