Tiller conversion?

[mainer4]

I have a 1963 28HP big twin cable only motor that I would like to give to my father-in-law to use on his retirement lobster boat just to keep him busy. It is cable steering only and he needs a tiller motor for his boat. Anyone have any idea how much of a job it is to make the change and what it would entail? Also, any lead on the parts to do it would be appreciated, I keep watching Ebay but not much luck on this old a motor. Thanks!

[boats.net]

Finding parts will be very difficult, not sure where to find them.