You need to hang out a bit on the Soviet Steeds forum. Get in touch with Immulmen (Chris Jordan). He has built TWO 750 flathead sidecar rigs that will cruise all day at 100kph. Chris did not use any special tricks when building those motors. It was just a matter of careful attention to detail. Your goal of 100kph for your K750 solo is a goal easily met. With solo gears, you will easily exceed 100kph. Drop by Soviet Steeds. It's mostly Ural stuff, but there is a dedicated group of Dnepr guys that hang out there.
Hope to see you there.