You can mount the radiator anywhere (in your case in the front) and use them as intake or exhaust.
The most efficient way is to use radiatiors as exhaust since the heat is removed from the case, but used as intake is also fine. Case temperature will be few degrees higher. Since you are going to cool only CPU, the difference between intake and exhaust is even less significant.
if possible (not all AiOs allow it) mount the radiator to the case and attach fans so they will pull the air through the radiator.
in that way you can easily clean the radiator from the outside (dust filters help to certain degree, but do not completely prevent the dust, fur , hair etc. from getting into the system).