Doesn't have an orange seat, can't be a Manxman !?
Breather coming off the end of the camshaft suggests a 750 Atlas engine. In 1962 and earlier, Norton used the title "Manxman" for all 650cc motorcycles shipped to all markets, and they did not all come with red seats, even the blue bikes shipped to the USA came with black seats late in the production run, for anyone interested in actual facts.......