Like, if you're willing to go mid-engined and base it off something like a Mark III VW, then yeah. It's entirely plausible. Stampie pointed it out with the rule "Any four-wheeled, production-based vehicle that was originally sold as a passenger vehicle is allowed." Now I haven't read any deeper into it, but the vehicle produced would have four wheels, be based off of a production car, and is technically a passenger vehicle as long as it's road-legal, carries at least one passenger, but has less than 9 seats (at least according to OECD, which the US is a part of). As long as it meets budged and can then be registered as a homebuilt, it can be in just about any shape or configuration you want. Since you're the manufacturer, it would be a limited-production car that can very well be sold as a passenger vehicle. It would probably be something Smokey Yunick would do, but it fits the "all original body panels" and "four-wheeled production-based vehicle that was originally sold as a passenger vehicle" criteria.