This is the Ninja radiator, slightly scuffed looking, and the 250mm "Works Power" fan that fits the size of the radiator nicely.

Most commercial radiators for water cooling computers are sized for 120mm fans, and to get enough capacity to cool the machine (which uses about 300W on full load) without loud fans, you'd need at least 3 of them. They also are kind of expensive. I figured the old Ninja radiator should have plenty of capacity (the equivalent area is about 3.5 120mm fans), and the huge 250mm fan should be able to pull a lot of air with low rpm. (It's supposed to do 105 CFM at 820 rpm with 19 dBA of noise.)