The problem I ran into with putting a 120 fan in the lower front is that I cut out the retaining tab for the front bezel.  It really isn't a problem, the case still closes and is actually a lot easier to get into now. 
You might be able to fit a 120mm fan without screwing up the latch but I got in a hurry and chopped away. 
 
A 90mm fan would probably fit a little better with less chance of messing up the bezel latch.