This looks interesting. The fan placement looks good but I'll tell you what I'd do. I would get another 240mm radiator and mount them both diagonally on the existing side fans. You could rig up a bracket that would allow them to fit diagonally (from right to left and left to right) so the inlets meet together and allow you to link both radiators together for perfect cooling. You could even add two 120mm fans to each radiator for optimum cooling.
Here's a pic I just drew up to explain my idea.
The black is the fan housing, the blue is the huge fans and the yellow is the radiators.
You would have to make a bracket to attach to the fans and then to the radiators, I believe this would be a very efficient cooling solution.