1973 XP-898
It looks a bit like post-1982 Corvettes, but the one-off XP-898 of 1973 was actually built on the chassis of Chevy's small four-cylinder Vega. It's mission was to test feasibility of a new "sandwich" fiberglass body construction using a foam filler that could be varied in thickness to provide desired strength in specific areas. Though it looks a bit dated now, XP-898 would have been a great replacement for the '68-vintage "Shark" Corvette in, say, 1975.