The problem is not the 300. I built a few computer with the 300 and I never had any problem fitting True 120 or Scythe Mugen RevB.
The problem is that the socket on some Evga board is quite close to the edge of the PCB. Some heatsink will let your install both horizontally and vertically. In your case, the heatsink horizontally with the fan at bottom, blowing up toward the 140mm top exhaust fan is a possibility I think.
Edit: If you install that way, make sure the heatsink will clear your memory sticks.