[stiletto2]

Is the top speed 50 mph because that is all it has power wise? (wind drag holding it back?) or (is it speed restricted or RPM restricted/limited) or could it go faster?

If it is speed limited I'm not so sure streamlining would be much help. (but I could be wrong about that... it is just my hunch, so...)

If it is RPM restricted/limited, then a solution for better economy might be a bigger front drive sprocket + streamlining... That would also be of help if it was actually capable of more speed simply with the addition of streamlining. Not that one would necessarily want to go faster per se, but rather for the economy gained from being slippery enough to afford taller gearing for lower RPMs at given speeds.