Synchronizing IC Temperatures
You don't want a heat pipe.  It is meant to transfer heat from one place to another, not to keep everything attached to it at the same temperature.

If you want to keep all of the chips at the same temperature, you want a high thermal conductivity material joining the chips together.  With unlimited resources, the best that you could do would be to thermal paste them to a solid chunk of diamond, which has the highest thermal conductivity of currently available materials.

Since that is probably not cost effective, the next best possibility would be to use Pyrolytic Graphite Sheet (PGS).  It is a layered material that conducts very well in plane, and not so well vertically.  The graph below shows a comparison of the thermal conductivity versus copper and aluminum.



You can google around for "pyrolytic graphite heat spreader" and find places that sell it laminated to a backing material for physical support, since it is relatively flexible.

Your most cost effective and easy to obtain solution would be to thermally connect all of the chips using high quality thermal paste and a copper bar as thick as you can afford.