Have you considered that the patina that the knife has is something that your dad may really like about it? If it was MY knife, I would not want it restored. My original hunting knife is an Old Timer, and the blood stains on each blade are to me one of the things I appreciate about that knife. It never fails to get me reminiscing about 'the sunny slopes of long ago' whenever I get it out and look at it. If someone restored it, I'd be pretty upset about it....I have plenty of shiny knives....but only one aged Old Timer....
Don't get me wrong, I appreciate your intent, just something to consider...