Geat detective work Helmut!.
If it's any help and you haven't seen it yet here's a link to documents and POP of an LS6 'Camino sold new at Grove..
Note the Zone is listed as # 81 and Dealer # 079..
http://ls6registry.com/bal/more/1368...800b1466xx.htm
If you haven't been to it Penticton has a large car show every year that may be a great place to check for leads on what you're seeking too!.
Got your email...very cool you hooked up w/ Tom Harris even though he had no info from the old dealership days!.
Keep digging!.
~ Pete