Thank you for your advice. As I think, the right cylinder is ok now, and I will try to settle the left cylinder valves within the same timings, without respecting the timing marks. Maybe Mr. Ernst Stärkle from Bale, who was a great motorsport enthusiast and imported Douglas postwar motorcycles in Switzerland, build up this engine with the sport-cams and just those parts, he found in his workplace. On 1948, he and his wife Margrit visited the Douglas-Workplace in Bristol accompanied with a dozen fellows from the Douglas Club of Bale, dressed as Scotsmen. I found this story in “Motorradfahren in der Schweiz, Band 2” published by the friends of ancient motorcycles, Switzerland.
Thank you very much!