Bolts that snap when tightening usually aren't seized in the threads. Most of the time it's bolt that,s been brittled by age. The punch and hammer trick usually works. If not, then Sears sells a kit called "Bolt-Out" that are a variation of the left hand twist drills. Unless the bolt end was spotless and oil-free, then the JB Weld probably won't hold, but worth a try.
