Is a JD 6.8 liter. Tier two I think.
S&W Diesel in Wilmington, CA (Los Angeles area) is a John Deere marine dealer and rebuilder. I'd call them and see if one of their folks will do it or if they can recommend one of the independent people they work with. Their number is (310) 835-3155.
When I was in the area I used them for Perkins engines, in which they specialize as a legacy line, and I still use them for parts. Basically, they were historically a huge Perkins dealer, and are still a specialist in their classic engines, but now sell, rebuild, and service the John Deere and Yanmar lines.
When I was in town I sometimes used one of their mechanics, Chris, and sometimes an independent Perkins specialist that they recommended, Martin Ball.
I don't know if Chris does John Deer. I don't think Martin does.
But, at any rate, I'd call them and see if they'll do the inspection and, if not, if they'll recommend someone.
When you call, Angel, their parts person, will likely answer. He may be able to help, but if not, ask for Scott, the owner.