Be careful about using AOI cpu coolers for other purposes. They are enclosed units subject to evaporation and air infiltration. Fluid levels will drop over time and refilling is difficult. Also, be wary of orientation. You want to make sure that the inevitable bubbles are not repeatedly drawn into the pump. So you want to position the radiator with the in/our ports lower, giving a low-turbulence chamber towards the top of the radiator for bubbles to accumulate.

Opinions differ, but 800+watts through a 2-fan radiator, in an already hot environment, is likely not enough. If this was an 800-watt CPU I would be going with either some wickedly powerful fans or 2x as much radiator.