I just got a Prolink Geforce 4 MX440 especially for this project, so I have a way to test the GPU block.
Here's my idea:
http://www.advancedcoolingsolutions.net/bruno/gpu.jpg
I have some questions about block position (inclinated to allow bigger size or "aligned" limiting the size to something around 1cm bigger than than the GPU chip itself). I'll post them tonight because I'm late for something now.
Thanks
Bruno Facca