I was considering that and will have to consult my machinist friend. If I ground the metal and filed it to fit properly without annealing those areas would no longer be hardened. Other untouched areas would be. (case hardening doesn't completely harden the metal all the way through) I think it would need annealed to re-harden the frame so I might as well go through the process of annealing, proper fitting and re-harden.
Thanks