Trimming the flange down is quite common. I used a bump box.. so I never needed to. Just do a little a time and check the fit often so you don't remove too much.
I think if you look around on the traxxas forum you can even find a picture of what the flange will look like after you trim it down.
Ok.. I went a looked real quick and here is an example. I wouldn't remove quite at much .. but you get the idea.
