Replacing the fan in ReadyNAS Duo - possible?

So I bought both, the Noctua NF-R8 (with 60mm-80mm adapter) and the Fractal Design 60mm (x25mm) and tried them separately under (roughly) the same conditions. The Fractal Design fan was slightly quieter but the Noctua with adapter cooled almost 10deg.C less so I'd recommend going with the Noctua over the FD. Don't use them together, they'll only interfere with each other and there's very little room in the rear compartment - it's almost as if my RN breathed a sigh of relief when I hoiked out the original fan. The only annoying noise from the ReadyNas now is from my 2 x 2TB drives (Hitachi Deskstar) which I've reduced the noise using WinAAM but might end up flogging and buying a couple of lesser 5400rpm 2TB Sammys.