Ok for the CPU. I would tap 4 small screw holes thru the cold plate into the corner of the block. This will allow me to use a 50x50mm peltier.
For the GPU....
I could use 2 50x50mm cold plates. The first plate would have hold tapped in the DD GF4 block. The second could tap into the first out side the 40x40mm peltier. Something like this....
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