A good machine shop can machine it for you. The end result is usually more efficient than stock, as they can put the perfect angled surface on. I have seen racers machine the sheaves to gain any advantage they can. Not sure about today's clutches, but the older ones were often way out.
2007 Dragon RMK 700 155", 2008 RMK 600 155", 95 Prowler 550 2-up, Really OLD AC Cheetah