haha nice! this is exactly where i bolted mine, directly on the second heatsink of the GPU, the one floating it fits great and you can bolt it directly to the heatsink since it got a space between each metal sheets.I personally cut a hole in the side of me Falcon, put a fan grill on it and soldered in a 40mm fan at 6v, bolted it to the 2nd GPU heatsink.
You don't need to do 12v fanmods on Falcons.
Just add an intake fan, replace thermal compound on the CPU/GPU, cut away the back fan mesh of the case, crank the fans up to 65/70% in FSD and you'll be fine.
Also, if you want a better heat flow, place a alluminum foil or thin cardboard piece, on the gpu's main heatsink, to cover the small gap between the heatsink and the fan's white plastic socket/case/cover.
and if you can, jtag/rgh it, and install freestyledash, you will be able to monitor the temps of the cpu,gpu,ram chips, and you will be able to see the temps directly from the start menu, so, you can see your temps at anytime even when playing games or watching movies