I think he quit doing the 7th gear because the parts became increasingly hard to find.
Unsure exactly which parts are needed, but know they come from another Kawasaki Motorcycle {Voyager}.
One thought is to find/buy the parts yourself and ask if he'll do the conversion.
But, a concern is "he moved and may not be set up to do the machine work".
NOTE: I am not speaking for him. You would have to talk with him first.
Ride safe, Ted