I suggest trying to find Vicki O’Connor, if you haven’t already.
She administrated both the Pro S2000 series, and pro Formula Atlantic, from the Chicago area all through the ‘80s. If Carl Haas Auto still exists as I think it does, that may be a start to finding Vicki or at least expanding your search.
At one point later on it was called the Oldsmobile Pro Series, or similar, and there was a west coast equivalent possibly called the American Cities Racing League (?).
With the lack of much Chevron involvement in S2000, it seems to me this may have originated as a Pro car — often the case with a marque trying to, Ahem, make its mark towards Club racing sales success.
Best of Luck! Many or most do not trace their car’s lineage, and that’s why history eventually disappears in the wind.
Edit: Perhaps you’ve seen, but some good history here:
https://forums.autosport.com/topic/8...-a-b52-or-b54/