Just make them out of plexi there man, no problem at all. Build the box type like those scoop shrouds that are sold. Then seal them as air tight as you can with some silocone to the rad.
I'd also suggest getting some 127x38 fans for the rad. They make most 120's look a bit sad. Papst makes the quitest of these monsters, no big surprise there.
For what it's worth to you I think you made a great choice of rad. That 2-144 having the 2.5" depth will help to maintain your pumps high flow. And that is the largest heater core I know of, without strange flanges on them, lots of great cooling.
What case are you using? And where in the case do yu intend to mount the rad and pump?
It's going to be one really good uber performer.
