Found some heat sinks that should extend the case's ability to remove heat.  Plan to mount these to the outside of the case when I mount the TO-220 driver transistors.

This is what I started with.  Looks like it could have been a CPU heat sink.
To give the middle heat sink a little more room I notched away some of the mounting ear material.  Also squared up the radius on the ears so the the first heat sink will fit a little higher.
Sides cleaned up a little.
Heat sinks cut in half.  The three halves fit perfectly down the side end-to-end.
Heat sinks laying on side of case.  Almost looks like it came that way.
Here you see how the heat sinks fit around the notch I cut and up closer to the mounting flange.