It depends on how much screw you can get to. Craftsman makes some really good screw extractors. They kind of look like a counter bore, but bite on reverse. You pin punch a center mark in the screw, lightly, just enough to put a dimple in to start the extractor and keep it centered so it doesn't eat the engine. Now using your drill in reverse, try to unscrew it out. If enough of the screw is showing, and the extractor is small enough, you should be OK. If the drill is down in the hole, you are going to have to spot drill the screw, using a tap drill for the size of the screw. This is going to bugger up your threads a bit, BUT. After you have a spot drilled in the center of the screw, then you drill a small hole and then use a screw remover ( different tool than above, this is a tappered spiral, again reverse pitch that you use with a small adjustable wrench or tap holder to back the drill out). If these two fail, you can chemically remove the screw, but that requires a full strip of anything iron from the engine, IE a bare crank case or muffler. I'm not going into this because at the moment, I can't remember what was used, but I think it is alum. You can check on some of the machining sites on Yahoo Groups and there is bound to be a thread on this. I just can't remember which site it was. I think Jobshophomeshop group.

Try to attach the photo again.

Don