My Hdd block is similar to
rotor's in size and function, although internally different as it was made with hand tools.
You really don't need to apply rocket science here as the relatively small heat created over time by a HDD will migrate to the block as long as it has some form of cool coolant flow.
I've not got around to mounting it to the hdds properly yet with the drives just sitting under & on top of the block as my PC remains in one place, but mounting would be similar to
rotor's method I guess.
build topic
HERE