Do you have a mig welder? I would cut the heads off about an inch down off of the original rods and splice them onto the new rods. Taper the piece you cut off and taper the end on the new rod. Weld the two pieces together. Then carefully grind and finish the rod shank or turn on a lathe.
I do have both a wire feed and a stick welder, have used them just enough to be dangerous. No lathe. Sounds like a job beyond my skills to be honest, but if my current plan just doesn't work I will give it a shot. Thank you for the idea, had not even considered it Dave.