I always intended to mount the drives to the HDD block using a copper plate on the sides too but never got around to it. I was also going to isolate them in a double glazed box to totally soundproof them as they can still be heard if listened to close up, but the Seagate IV's in single platter are so quiet it really isn't a requirement. They are truly the only item that makes a sound in my PC when not using DVD/ Printer etc, (unless you include the slight component buzz of the NF7-S).
From my experience cooling two drives via the top plate works just fine, we are not talking CPU point heat levels, (at least not with 7200rpm drives), and heat will always migrate to a cooler surface as long as there is some type of transfer medium. My opinion is don't complicate it or over engineer, just make a block that works well in your system. I choose a slim flat block simply because I could cool two drives with one block. Oh and one other tip, do not hard mount your drives as doing this with mine makes them 10 times more noisy, (especially in seek). If the seek noise is annoying try just sitting the drive on some foam for a test if you currently have the drives hard mounted, and see if it makes a difference in your system.
I'm going to make a new HDD block soon to complete the migration to 8mm festo for all the blocks. Not important but a slight correction in that my current HDD block has 6mm festo push fits and is constructed using two 2mm plates for the top and bottom and the main part is 6mm (not 10mm), making it 10mm thick overall.
