I've got the Johnson pump (as you know
), and it's a tad noisy. The Eheim however is overpriced for the pumping capability, which is no match for the Johnson one. If you've followed the Johnson pump thread, then you know that it's a good 12v pump, and easy to adapt and run.
As for Cathar's block, you'll find ordering info in the "Extreme Cooling" forum of OCAU: that's the origin of it.