Do you have any bondo? you will need to fill along the seam and sand. Don't use more bondo than necessary. Go slow when cutting out the visor so that you don't need to rebuild any spots. Hopefully you have a dremel and some type of power sander. WEAR A RESPRIATOR!!! and of course take your time and HAVE FUN
I just went out and bought a Dremel (along with a respirator and goggles). Thanks for the advice. wish me luck. I know I always like to see people post progress of their helmets so maybe I will do the same.
If you can, try to get yourself a Black & Decker Mouse handheld sander or similar. I highly recommend one. I am in the finishing stages of filling and shaping my MS Fett helmet and the Mouse sander helped to keep the ear sections square. I am currently shaping the dome and filling in the dent (making prepro "eyes" version) and it is even coming in handy for that.