I'm a newbie to the site and looking around, spotted this nice thread and video. But a correction - the civilian Sport Scout was a conventional 45 cubic inch V engine like the Chief. Model 6XX with the last two numbers the year model. Attached is a picture of my 1941 640. Similar to the Harley WLA but with standard (for Indian until '48) left hand throttle and right side hand shifter. Indian only made 4,400 military 45 inch Sport Scouts, and Harley made over 80,000 WLAs. The government forced Indian and Harley to not put the year model in their serial numbers. I have heard this was related to security and concealing production. So civilian Sport Scouts were models 639, 640, 641, 642, but the military bikes were all 640. So serial number 640XXXX even if made in '42, which was the last year for civilian Sport Scouts by the way. All wartime WLAs had serial numbers 42WLAXXXXX or Canadian version 42WLCXXXXXX. 841 was the prototype to answer the Army's request for more of an off-road bike: rear suspension, foot shift/hand clutch, both cylinders out in the air, and shaft drive. Indian made 960 841s, engine like a Scout turned 90 degrees. Harley made 1,040 XAs, the engine being a decimal-for-metric copy of a '38 BMW flathead although they never admitted it. There is an XA in the video. The shaft drive bikes never went much beyond the testing phase because by late '43 the government knew where the war was going to be fought and it wasn't going to be in the off-road oriented Middle East. Also the jeeps took over some motorcycle roles so fewer were needed. Indian converted their 1930s 30.50 inch Junior Scout to a military machine called model 741 but the U.S. only bought one. Not fast enough. Many went to the UK and Commonwealth armies especially Australia and New Zealand. They wanted 500cc maximum. Indian called it Army Scout. Looks much like a 640 but with six obvious visual differences. Indian called the 640 military bike Sport Scout like their civilian model. Technically, all of these had a -B suffix indicating battery ignition. M meant magneto, no battery, normally racing machines, like 640-M. There... more than anyone wants to know.