When a flat twin is mounted transversely it creates several problems. For starters, the widely splayed cylinders demand their own carburetors. These have to be hung off the back of the engine, which intrudes on footpeg space. Second, ground clearance is always an issue (especially back in the day when bikes were a lot lower). Third, some riders are put off by the torque reactions of transversely mounted flat twins, even though any issues are usually perceived to be more of a problem than they are. H-D resolved these matters by arranging the engine longitudinally-and no, rear-cylinder cooling wasn't a concern.