That looks pretty good.
Two points of interest, the nice big flat metal surface is insulated from the resto of the drive by an o-ring. It may look like a good place to stick a waterblock but you can do better.
Also, think about HD manufacturers. If you have a problem with heat management, users will be screwing a large piece of metal, (your case) to the sides of the drive. I have heard that they do try and get the heat to the side of the drive, this being one of the reasons why.
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