Since you have a FEL you should be OK. If it starts to feel light you can always scoop up some dirt to add weight...
My BX2200 does feel light in the front if I have something on the back, and do a quick reverse to forward transition. I don't have a FEL or front weights, but I do have about 40 lbs of foam in each front tire.
In your case all should be fine.
Edit: I see you were asking about NOT having the FEL on... /forums/images/graemlins/blush.gif /forums/images/graemlins/blush.gif /forums/images/graemlins/blush.gif
As I indicated above, with about 80 lbs on the front of my BX, and only a light duty rear blade or 6' landscape rake on the back, mine feels VERY light in the front sometimes. I would expect with 400 lbs on the 3PH you will not like what goes on at least part of the time...