Right, lose the 120.3 and get a 120.2 for a start, yes it will make a tiny difference but its certainly not the be all and end all and doing it my way will save you the hassle and expense of building a radbox.
Excuse the ghetto pic but I can't be arsed to do any better..
Tidy your cables, rest your pump on the bottom shelf of your case with foam mounts to kill the vibrations and voila.
I did say this earlier but the only thing you'll remove from this by getting a radbox is the pump and rad, the pump can be houses very easily (or maybe even get an mcp350/res comba as seen
here (available at ocuk) and then you only need to house the rad..
Cut a hole in the top of your case easily for a 120.2 (if you move your top ide drive down one then you'll get a 120.3 in there I'm sure) or hang it off the back of the pc using fanmounts or homemade standoffs.
Stop fannying about with a radbox, and to correct marv(
), I had TWO loops fully cointained in a pc65 which is about 75/80% of the size of your case. Get tidy in there and I reckon you'll find acres of space.