Is that thing really tight in there? if it isn't, it looks like you could cut a groove in it, and screw it out. If you intend to drill into it, first file or grind it really flat, then use a tiny punch to make a small dimple right in the middle of it, so the bit doesn't slide around, and go down between the threads. Remove the engine if you have to. Once you get it out, replace both bolts with 8.8 bolts, or allen screws. Peace. Jerry.