Hi,
I can try to help. I have both the Antec 300 and the Mugen-2 though I don't use the Mugen-2 in my Antec 300 case. The A300 case has excellent airflow and the Mugen will work very well with the fan blowing toward the rear of the case or upwards toward the 140mm fan. I personally have a Xigmatek HDT-S1283 in my A300 and have the fan pointing upward.
Your Trident memory might cause you some difficulties as the Mugen is a very large cooler. I believe the dimensions are 120mm by 130mm. In my Antec 1200 case (with the Mugen-2) my first ram slot is covered by the cooler. I use OCZ Gold memory dimms. Can you put the dimms in any slot? You can try that first. If memory serves me right, you might be able to mount the fan blowing upward to leave room for the dimms if they have to use the first slot. Either way, it will serve you well and keep your CPU cool. Good Luck