Since this is a C.O.M. revolver, if the hammer is replaced with either Pietta or Uberti parts (which are CNC machined these days), it might need a bit of fitting since C.O.M. has not marketed a firearm for over 3 decades, none of those revolvers were CNC, and tolerances varied quite a bit since several small shops were involved. I am not aware that there was ever a source of parts for these revolvers, either.
Regards,
Jim