Hmmm, there would still need to be heat transfer inside the heat sink from one side to the other via the bottom plate. Maybe that would still be more efficient

Hmmm, there would still need to be heat transfer inside the heat sink from one side to the other via the bottom plate. Maybe that would still be more efficient than the transfer via a larger contact area between two heat sinks back to back? Not sure...either would probably work. What I can build might depend on the geometry and size of the heat sinks that are easily available. One big heat sink would make construction a little easier.