The only way you can use 120 fans is with modification to the radiator or using zip ties. I strongly advise against this. If you want to use the fans that come with that case buy the kraken x52 version. It uses 120 fans.
Only 140 fans will work as that’s where the holes on the radiator are positioned. You wouldn't want to put 120's on there because you won’t get the full surface area for maximum cooling. If you would prefer to use 120 fans I would suggest buying the x52 version.
Okay after doing more research people are saying you can fit 2-120mm fans on a Kraken x62 but would have less air Pressure which in my Opinion I don't think it would at All due to the Simple Fact that 120mm Fans Have higher Static Pressure than 140mm Fans
The only way you can use 120 fans is with modification to the radiator or using zip ties. I strongly advise against this. If you want to use the fans that come with that case buy the kraken x52 version. It uses 120 fans.