I would check some of the hard to replace items such as the torsion bars, and the front sway bar. If you know what an early A body sway bar looks like, that would be a pretty big giveaway, as they’re not easy to find, and not often installed to try to pass off as a real S car. Torsion bars too, and of course the “31” must be there, that is the 4bbl motor designation.