I wonder if someone could tell me, would an original 1968 Norton fast back in green with grey side panels have any writing on the side panels???
A quick check in Mick Duckworth's Norton Commando book (pages 49-50) indicates 1968 models were plain silver.
1969 models do have a decal '750 Commando' on the side panel, e.g. http://www.classicbike.biz/Norton/Brochures/1960/69NortonCommandoBrochure.pdf
Articles in Motorcycle Mechanics from 1968 and 1969 included in the Norton Commando Ultimate Portfolio also support this difference.
Andy, thanks for your advice, really appreciated.