#462553 Well, close but no cigar.
It's actually an Opel, the Genèva Concept from 1975, but obviously closely related.
Was planned with a Wankel, too, but finished after the oil crisis with a Chevy-derived Opel Diplomat 5.4 Litre V8.
AFAIK the XP978 proto is sitting in the Corvette Museum in the USA.