Who was your guy that passed, Gary?
You'll find out fast a bunch of shops/ guys are gone and few are taking the cars on anymore in general. I found a local old timer I trust to do a bunch but the big stuff is where you'll be in trouble. Literally call up places and see who's got some real long term experience, anything over 20 years with GM will be useful if they're still a quality mechanic.
While everyone talks about Rick I've yet to get in after 6 attempts, don't know personally.
Tommy at A Alert in Chicago is still around and doing LS conversions too.
Sound Performance in Bensenville wil actually take the car in quickly but with Sean gone they don't have anyone there that knows much about a GN (mechanic wise) (Larry the owner tunes them though and seems like a trustworthy guy). They're rough with electrical work so no recommendation there unless maybe Larry does it.
I'm trying to get my DSM champion mechanic to start with GNs, he's taking mine on in a week to fix all the electrical gauge issues SP created and didn't resolve. Hopefully we'll have a beast from Schaumburg willing to wrench on GNs. But like all great mechanics, he's slammed with long waiting lines to get in. But if he does he's no doubt a champion to trust and do things right, I'll report back.