Finally found something that could make that possible, but I think wouldn't fit 420mm because the mount would just be too long. 360+240 60 should be enough, right? Any recomendations on the pump?
http://themodzoo.com/forum/index.php?/topic/775-diy-case-mod-guide-280-radiator-in-fractal-design-r4/
They seem to fit it nicely but that's a one with the smaller end tanks?