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

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!