I just looked at one of the buckhorn sights that I removed from one of my Marlins, there is a blade that you can adjust for further elevation after you have already adjusted the elevator. Also like mudhen said, you could replace front sight with a taller sight to bring down the impact of your rounds. Move the rear sight in the direction you want to go for windage. Personally, I would put a receiver peep sight on that rifle, and I believe your Dad will really like it.
