I looks as though the original bolt handle was bent to the rear and knob added. I would think that it would be comparatively easy to reverse that procedure, by removing the knob (brazed on?) and re-bending the rest of the handle back to the original vertical position.
Whoever does this job should be able to improvise a fixture which would allow the bolt body to be immersed in water during the entire procedure. This will protect the body of the bolt from the effects of the heat applied to the bolt handle.
