The Hinckley twin has the potential to go to 1000 cc's, or thereabout, as the American flat track racers have shown. (Think stroker crank, along with bigger bore.)
That should be plenty to haul that lighter-than-Jap. frame down the road in a respectable manner. It should even out perform the 1200 Sportster.
More horsepower is not what's needed, but more, and spread out torque is. All this is do-able within the confines of the current vert. twin engine design and not require a completely new engine attempt.
NOTE: You youngsters will have to learn not to rev the snot out of such an engine, though. <chuckle>
