not sure to be totally honest. I'd guess Chrysler did it themselves with the Sebring and Probably GM with the 4g F body. Don't quote me on any of that, just wild guesses to be honest.
as for the lack of quality.... lol that was name of the game then. 80s custom cars were a real shit show. Ask any GNX owner to see inside the rear wheel arches, its a mess. I've never seen 2 Turbo Grand Prix that were exactly the same either, they were factory hack jobs by ASC. It was the wild west then. Pop rivets, self tapping screws and cut body structures lol