to add watercooling to your card, you are going to invest ~ 100-150$.
If you are doing it to get more performance, don't. You are going to get 50-100MHz more at most, but not necessarily.
If you do want more performance, just sell you card and get GTX 1080 for about the same investment with much more value.
You can get quieter and cooler system. If you after that, then you would be better using blocks designed for the GPUs - they are slightly different due to the fact that GPUs have exposed silicon which better contacted with flat blocks. CPU blocks are not flat.
The suggested above EVGA Hybrid will not work as it seems that your card has custom PCB. Beside cooling the GPU, there is a vRAM and most importantly VRM.
So your options are...