Thanks for the kudos everyone. A friend of mine suggested that I make the little piece on the handle from Walnut also. Thinking I might give a try. I dont know if I can remove the handle.
The pin that holds the knob appears to be riveted into the crank arm. You could try splitting the existing knob off. Then on the new knob, turn it, either saw in two with a thin scroll saw blade or split it on the grain then glue it back together in place, sand and finish. A lot of work for a little knob.
You might try simply sanding the existing knob, staining darker and finishing.
Good luck!