^^^^^^^^^^^^^^ Don't think he wants to take off the heatsink.
I would just change it to this as it really shouldn't effect performance to the stock setup.
Top fans usually blow upwards. Make sure the fans blow in the same/similar direction so either turn your heatsink to blow back in your case, or just move the fan to blow up. Blowing air down onto the GPU is rarely ideal because it is pushing air away from the exausts. With a top fan blowing down (like a SG09) the tower heatsink should push air back.
Wouldn't the efficiency be significantly decreased in that config? Typically you have your front fan bringing in cool air to the CPU heatsink and fan, but there all you've got is the hot air rising off the rear of the GPU.
It'll no doubt be AOK, but the temps will be higher, which will mean the fan has to run that bit quicker to keep everything cool under load.