Thanks so much for the advice Moto.
The reason I wanted to make the block is because there is little airflow in my case and I'm aiming at silence. I haven't discarded the idea of modding the HD bays to have a 120mm fan to cool the 2 HDs I have, but I liked the idea of delving into waterblock crafting, so I'm taking a plunge at it. Furthermore if I later decide to isolate the HDs and put them into foam or boxes, the hd waterblock would be great to keep them cool.
Thanks for the link to the copper plates, that’s probably the cheapest I’ve seen, almost on par with the eBay prices I’ve seen but in better condition. I might change the design though and require thinner copper. I don’t like the idea of a monster tall HD waterblock, we’ll see.
I found a nice and cheap
SAE Tap and Die Set on eBay which should do the work fine. Thanks again.