The part that many folks may not be aware of, is that the 'duplex' wheel cylinder/ single pivot drum brake arrangement has both a 'leading' shoe and a 'trailing' shoe.
  Due to the rotating action of the drum, a leading shoe's lining (different on each side) gets a stronger 'bite' against the drum's braking surface, due to a 'wrapping' effect.  The trailing shoe has a lesser bite for the same reason.
  So, your rear brakes will have an actual effective action that's dynamically better in motion, than while watching it operate while standing still.  
   BTW, the split window bus front drum brakes had two simplex wheel cylinders/ two shoe pivot points, so that both shoes were leading shoes.  Incidentally the rear drums were the same duplex arrangement that carried through the bay window bus, and onto our Vanagons.
  As a side note, 356 Porsche front drums were aluminum with steel friction surfaces pressed inside, and dual simplex/ leading shoes.  The rears were still duplex.
  This shows that the rear brakes on most vehicles are needed to balance the braking forces, but must not equal or exceed the front brakes effectiveness. The optimum ratio is normally 70/ 30 front-to-rear braking power.  
  The bottom line is that our 'hokey' rear drum brakes are plenty effective enough to do the job properly.  Any major improvement may actually cause unsafe front-to-rear balance during heavy braking, and could result in loss of control as the vehicle tries to swap ends with the rears locked up prematurely.

Mike B.

  How Scott (turbovan's) got his brake shoes to wear evenly is beyond me. Based on the design I think it impossible.  Mine very clearly show about one third of the shoe being used.
  Troy