I looked up the GTX and it's 10.5". The Tsunami leaves very little room beyond the motherboard. It's easy to install because the drive bays are removable, but it really looks like a GTX would be pushing it. Check
this review and you can see some pics with the MoBo installed and you'll see what I'm talking about.
As for modding the 3.5 rack, yes, probably need a little dremel work.
-Crom