I am rather surprised to hear that your crankshaft may have ended in a left hand thread. That would be a first for me, I've never heard of such a thing. Clutch shafts sometimes, though rarely, end in left hand threads to carry the chain sprocket, but in my experience never a crankshaft. It is commonplace for crankshafts to have a thread on the flywheel end to retain the flywheel, but it has always been right hand in my experience. I can't currently recall an external thread on the drive end of a crankshaft - the part that Briggs call the Power Take-Off, and everyone else calls the output shaft. They conventionally have either a parallel shaft with a key, or a tapered shaft with a key. Often they have an internal thread for a securing screw to hold a drive flange.
Can you post a picture or two of the damaged crankshaft? We may be able to devise a way to repair it.
