Damn, that sucks....well I hate to say it but you can try to re-tap it if there is enough threads to grab, but if that doesn't work I would think you would have to enlarge it to the next size bolt and then tap it, you would also have to enlarge the holes on the pulley, do all 4 if it comes to that, sorry that's the only thing I can think of.
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My Ride Check Out My Site 91GT, Holley SysteMAX II Kit-Heads 2.02" x 1.60",Full MAC exhaust 1-5/8" Long tubes, 2-1/2" O.R H-Pipe, 2 1/2" cat back, 12" K&N Filter, RNH PERFORMANCE Ram Air, Ron Davis Radiator, Full Suspension,3:73's, Welds, Best on new motor-12.60 @ 108, no traction 1.98