I wouldn't mess with any of the bolt extractors .... none of that stuff works all that well in this situation. Just get a drill bit the size of the outer diameter of the screw and drill the head right off the bolt. That will free the mount from the arm. Then raise the engine until the arm extends above the mount and unscrew the bolt from the arm by hand .... since there is no more tension on the bolt it will just twist off by hand. If you don't have enough clearance just remove the arm and then unscrew the bolt. It's fairly simple ..... I have had to do it more than once to correct previous shoddy work by others.

David Roseman
Long Beach, Ca