Hi BDD, I am in Jackson which is just north of Milwaukee. I have a Manta and a GT. There is Bill Hoffmann who lives in Wilmot, just west of Kenosha. There are quite a few of us in the greater Milwaukee area. We are planning a get together in the next couple of weeks or so to formally meet each. So far it has only been by emails. If you are interested let me know and I will forward the info to you. By the way, there is an orange GT parked next to Hilltop hardware off of Kenosha highway 158. If you are in the area you may want to check it out. It appears to be parked for quite awhile.
BDD, does the black GT have side pipes? If so, I know where it is from. He is from Mukwonago. I saw it in a garage while garage saleing a couple years ago. I don't know if he is a member here. I talked to his wife a few minutes and mentioned the site.
I'm in Sheboygan Falls. If you find yourself over in Elkhart Lake at Road America there is a good chance I'll be at the track either in SCCA support or as a spectator. I live just down the road.
If you are looking for specific parts, I know a guy up in Little Suamico who has several GT's all parted out and in dry storage. Multiple pieces of almost everything mechanical. I'm not sure about body work. PM me and I can give you his contact info or you can search for Green Bay Craigslist for "OPEL" as he frequently posts that he has parts available.