I know but surely the heatsink cannot go on top of the CPU if the CPU cooler is there
I think you are just getting confused with your terms. a CPU cooler can be a air cooler with a heatsink and fan, and also a liquid cooler with a heatblock, pump, radiator and fan.
To answer your question, with the H60 you no longer need your stock heatsink and fan.
I know but surely the heatsink cannot go on top of the CPU if the CPU cooler is there
I think you are just getting confused with your terms. a CPU cooler can be a air cooler with a heatsink and fan, and also a liquid cooler with a heatblock, pump, radiator and fan.
To answer your question, with the H60 you no longer need your stock heatsink and fan.
If you were to buy the water cooler that you linked to, you will not need any additional heat sink. There is a small water-block that mounts directly on top of your processor, and cools it through the closed loop radiator.
They are easy, assuming your case has the hole in the motherboard mounting tray, so you can fit without taking the mobo out. (some cheap or older cases dont have the cut out).
You won't need a stock cooler on top with an aftermarket CPU cooler. That corsair hydro series will go on top of the CPU itself. Anyway not really in to liquid cooling, I think air cooling can get you a perfect temperature too with overclocking!