Thank you for the info, Dave & Brian.
Dave,
Well, I really do learn something new everyday! I always assumed that by the 1970s, INS units were S.O.P in pretty much all trans-continental birds...particularly including BA VC10s. Thanks for the info! I was only 6 years old when the Falklands conflict broke out in '82. I actually remember the date fairly well...since my dad was still in the USAF then, and was coincidentally building a rather large-scale plastic BAE Harrier model (Hasegawa? Monogram?...can't recall for sure). He gave me a complete junior-league rundown on the plane & conflict then. Ahh...family memories!
Brian,
Thank you, as well. Might I mention that I am jealous of your experiences?

I've got my PPL here in the US, but haven't flown in nearly 10 years...and the only 'jump seat' observer time I've ever logged was a brief 45 minute flight in a Hawker 800XP when I worked for NetJets in Columbus, Ohio. Sadly, that's the closest I've ever come to a "classic British" flight experience! What I wouldn't give for a jump-seat on a Comet...or Brittania...or Trident...or 707...or DC-8...or 747...or (list goes on and on!)...