The XSPC Rasa 750 RX360 kit would be a great investment into watercooling. The price is right for what you get (fantastic value), and you'd only need to add a waterblock, of which XSPC makes great 6970 waterblocks as well (I own and use 2 of them on 6950s).
You're looking at about $190 + $90x2 + $8x2 for barbs for the 6970 block + $17 for new tubing (buy yourself some nice Primochill Primoflex in your favorite color in size 7/16", available from Amazon as well as other sites) + maybe some good thermal compound, like Shin-Etsu X23-7783D.
With that, you should be good to go, and have a really rockin setup. I've got a more dense radiator than you, but I keep my fans lower, so it doesn't end up dissipating as much heat as the RX360 does, and my CPU temps rarely reach over 55c (2600k overclocked to 4.3ghz, stock voltage), and GPU temps never reach over 50c unless I'm running furmark which punishes cards like nothing else, but isn't even a good measure of stability.
Do you run eyefinity or something? I can't imagine two 6970s being necessary for a 24" screen. I only got it after seeing my single 6950 heat up like no tomorrow and framerates plummet when I was running 3 1920x1080 monitors in eyefinity.
Either way best of luck! Watercooling is a great adventure if you like to tinker.