3. XP-819 Corvette
Had that Ford GT come into existence, it could’ve had company in the form of this rear engined* Corvette. However, this particular model never made it—though GM made several other rear-engined prototypes in the '70s. Rumors have been ebbing and flowing about a mid-engined Corvette coming to fruition for 50 years now, never more so than the present.
*Technically, this one's rear-engined, not mid, but the mid-engined cars that followed were essentially evolutions of this concept.