With my Thermalright ultra 120 I cannot use a side fan. I'm tempted to have a go at modding the fan to make it fit. It is only one corner that is in the way. I think the fan has enough clearance to make it.
Why in the world do you want to do this?
I have 6 case fans in my tower; and no side fans at all...
I'm running a e6600 on a P5WDH at 3.7 and under full load it once in a while peeks at 55 for brief periods of time.. most of the time its at 43