So, all you need is a convenient induction heating unit! I was a little surprised at the straightening that was done. Assuming that any distortion would occur in the annealed section or at the boundary between that and the "left hard" section, wouldn't any slight loss of straightness be taken care of in the machining? If you are using the untouched threads to hold the screw (decent collet, etc) then I would have centre-drilled, brought up my tailstock centre, and just turned to dimension, confident that the turned part was going to be concentric with the body of the screw. What have I missed?

- Brian