Just so you know, you could just fit the Hard drives in the 5.25" bays with something like this:http://www.performance-pcs.com/catalog/index.php?main_page=product_info&products_id=4475
That should give you the clearance you need. Also, not case can tame a GTX 480 like an RV02/FT02.
Also, can I see your mobo? There shouldn't be a problem unless the last PCI slots are used...I can't see a problem arising since that is 4 4870 X2s, which are notably longer than a GTX 480: