I'd go the other route and up-size the blower pulley. Reducing the belt contact area on the crank pulley and a small blower pulley can get into potential belt slippage territory. Keep the stock crank pulley and throw a bigger blower pulley on and that'll help maintain the largest area of surface contact for the belt on both pulleys. That should relieve some stress on the belt and give you a good chance at not seeing much belt slippage under load.