Cut the outboard 3 inches off the spindle, drill and tap the stub, and make a new outboard end that screws into the original part. Then you can duplicate the original thread. Cross-pin the repair stub to prevent it from coming apart. That's "machine shop 101" stuff. We were making custom spindles for round track dirt cars 60+ years ago, and they are subjected to far more load than any street vehicle needs to handle. Most of the tool and die people I used to work with could identify steel alloys by touching them to a grinding wheel and looking at the sparks.
Jerry
