I found this an interesting, but confused question (since I have no idea of the stance you use). I brought it up in conversation with some other fighters and coaches at a dinner (Yeah, that's all we like to talk about, so our wives encourage us to get out away from them). The consensus was that in the proper stance and head position, it should not make that much difference. If it does however, then the suggestions ranged from slight move of the position of the head, to adjusting the stance. In short, no one could give a definate answer without being there to physically see your stance, your punch, and how you move. I guess the best course is to have your coach give you an evaluation. Changing from a right hand hitter to a southpaw is a radical move that might not be the best for you.