wow.. 8 hard drives?? boy.. i had no idea.
My banter was based on my system which sounds like 1st grade to your advanced setup. In mine I have one hd, one cdrom. I put the heatercore inside and with good fans pushing air into the case it will have enough to move the not so hot air out through the radiator. It achieves what I want in the setup.
I see your delimma though. With all that equipment an inside heatercore may not be the most ideal place for it. I yield my naive rantings on to the more experienced. You would really have to get some fans moving in some serious air. Then your noise level would go up unless you bought the perfect fans.
Consider
This THREAD. It shows a link to a case like product with power. The pump and rad are stored in it. Perhaps this would be the soltion you could use. Possible even stack it under or ontop of your case.