The dimensions are correct for a B tonneau.
The snap configuration would appear to be correct for an early B factory optional tonneau, as is the color.
The snaps across the middle button down on the heelboard behind the seats.
Tonneau color initially was the same as the interior trim color, so this one would have been from a car with a red interior.
Oddly enough, I have such a car, with a black aftermarket tonneau.
...???