WC 2x6990 in 800D internally

I've decided on going water cooled so for the last couple of days I've been reading up on the subject going through forums and guides around the Internet. I've build a couple of rigs but I have never done WC before. Therefore I would like to keep things as simple as possible... the part list look like this (excluding the WC stuff):

Chasis: Corsair Obsidian 800D

CPU: Intel Core i7 2600K Sandy Bridge

MoBo: ASUS MAXIMUS IV EXTREME-Z

SSD: CORSAIR FORCE GT SERIES 3 2.5" 120GB SSD MLC

PSU: CORSAIR AX 1200W PROFESSIONAL

RAM: CORSAIR 12GB DDR3 1600MHZ (6X2GB) CL8 DOMINATOR WITH DHX+ W/ FAN BLUE FIN

GPU: 2 x Radeon HD 6990

Display: 3 x Dell 24" UltraSharp U2412M IPS Panel

Here was I was thinking: I'd cool the CPU with a Corsair H50 Hydro Series and then add a single water loop to cool the 6990's.

Questions:

1. Do you guys think that it would work?

2. Would a 360 rad on top of the case be enough to disperse the heat from the GPU's?

3. How would I ensure that there is sufficient airflow with the H50 and the rad mounted seeing that MoBo/RAM is air cooled?

I don't plan to do much overclocking (maybe down the road). Would just like to keep things cool and relatively silent. And I don't wanna mod the chassis (looks really awesome as it is :-) ).

Any help/suggestions will be much appreciated!