there're 140mm fans with 120mm screw holes, make sure it doesn't nudge other components first. Rather than use 140mm (with 120mm mounting such as silverstone fan) you can do push-pull, one fan is pushing air and one fan is pulling air. As mike said, H60 has weak pump (low flow rate and weak static head pressure pump), to increase cooling capacity you can also use top TIM such as Hydranaut, Arctic Silver MX5, and use better case fan to get maximum positive air pressure of your case.