Ford Lehmans have been put in a LOT of boats for more than 20 years. It would be hard to think any good desiel mechanic
couldn't do the job. They are not that special. Finding a good mechanic is mostly asking around and checking references
You really want one within an hour of your boat. Most will charge travel time if they are any good. The best mechanics I've ever used did not work for a marina but were independant. Some of the worst ones I know of work for a marina. The "Great Lakes area" is pretty big.