I've got a plan now. I may get hold of just the chassis for a Shuttle SB61G2 (I can for £25), as shown below:
I'm going to 1 rad at each end on its side, so the shrouds are protruding from each end, and have them both blowing out of it, so there's a vacuum in the middle of the shuttle case. I'll drill 120mm blow holes in the sides of the centres, and put my MCP600 in it. And I'll also cut a gap in the bottom of the shuttle for the wires to come out. But it'll also act as another air intake, sucking air from the PC below.
Do you think this is a good idea, or should I screw that idea?