I'm not disagreeing with you; but I'm in horizontal Lifan (z50) 50cc Honda clone, (with E-start, and auto shift; it's the only way to get it recognized in many states as a moped/motorized bicycle, and that varies from state to state), no jackshaft req. Many places have chains (420), and sprockets (bolt on type, to single speed freewheel (worksman), fitted to the hub). Personally, I feel Alan's bike is a beautiful bike; but I'd like to have seen it a bit longer, maybe 5" on the bottom tube. I do like how he's got the BB so far forward, I need to stretch my legs, (first, to get maximum power, when needed. Second; my legs were busted up in the Army, and I can't have them all bent up for long).
As far as the power loss goes, as with a m/c, I think it'd be negligible also... Do you think it would be better with dual shocks? If I designed that bike, I'd have made the bottom tube, a bit longer, to allow for the 18" or so, needed for the horizontal push, 4 cycle engines, as previously mentioned.