When you remove the fan trays you will see there are rubber quick release tabs(outer side of tray sliders) that you press and that will release the tray from the sliders. If you had done that with the top tray you would not have had to remove the back slider assembly from the case.
Disk at other side looks like base radiator but it's not. It's just a dummy after I realised it I did not go for buying this. And I bought creative pebble 2.0