Remember the guys at BSA were interested in selling bikes made out of parts they had rather than consistency, and correct for that year's specification. Also the airbrushed photo artwork in the catalogues is a mock up rather than a real bike. The same base picture is used for every variant.
I would try and find photos of the bikes at the time. Maybe copies of the motorcycling magazines from the time would be more help.
I believe Classic Bike now has the full photo archive from those magazines and you can order prints.
Cheers,
Iain