I may have jumped in here a little too late, but we have encountered this problem many times in the past. We have used a solid steel rod thru the holes in the pully and put a 3/4" dribe breaker bar on the bolt. Select the largest hammer in the shop and give her a BIG smack on the breaker bar. 2 or 3 hits, and she breaks loose. Remember to use some proper thread locker on the bolt when it is reinstalled. And torque to spec. This bolt, as well as the axle nuts are two problem bolts/nuts that seem to get over torqued in some shops.