US$23,765.50 Douglas 1920 4 HP 596 cc side valve flat twin Frame # 12657 Engine # 11612 This Bristol-based firm developed the horizontally opposed fore-aft unit in about 1907 and continued utilising this engine layout well into the thirties.The earliest Douglas models had direct belt drive, but in 1910 a two-speed gearbox was added, with the control on top of...