The only mod I have done to my 500 is to mill the slide slightly. This added a little snap to off idle response. I would think that you would need some porting work in order to accomodate opening the carb to 40mm.
Maybe someone else has experimented with this change. I'm note sure I would risk the price of a Carb to see if it would work. In fact, before I shaved my slide, I installed one that had already been modified to ensure I liked the difference, that way I had no risk. You might want to think about finding someone that has done this mod, and find out if any motor work was done before you hand over your carb to the machinist.
Good luck
Rick
