If you're going to replace the drive bay res, it's possible to fit a 120mm rad in 4 x 5.25 drive bays with an adaptor - any 3 x 5.25 bay fan adaptor and just attach the rad to the fan. Extra cooling and spares you having to dremel a big hole out in the roof .
It is something I'd thought of, but I'd probably prefer to use the space for HDDs.