I don't believe there would be a version of the Negus livery that said BOAC. It incorporated (somewhat) elements of both BEA and BOAC liveries, as the post-1974 merger colour scheme. It was the other way round, the previous separate company schemes were initially rebadged as British Airways or British Airtours. These seem to have lasted for some time; there's a photo of ARWD still with the old BEA colours (but KT titles in the new font) on Airliners.net dated 1978.
One 707 we have missed is "Spread Legs" (OK, Sierra Lima), G-AYSL, a 707-321 (old JT4A straight-pipe engines) which BA took from Dan-Air and which ran in 1978 in mainstream BA titles, then in the 1979 season transferred to Airtours at Gatwick. As well as non-standard engines for the fleet it had it's own non-standard livery derivation with a grey under-fuselage as well. I wonder what it did out of Heathrow initially.
Photos: Boeing 707-321 Aircraft Pictures | Airliners.net