It looks a bit like post-1982 Corvettes, but the one-off XP-898 of 1973 was actually built with components from 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.
The chassis and the body were one complete unit, there was no separate steel or metal chassis. There were metal attachment plates that were enclosed in the body material (as a sandwich). The XP-898 body supported all the functions of the chassis that you might find under a Corvette or any body-on-frame vehicle. In a sense the XP-898 was a monocoque sandwich.
Thanks Paul Villforth for the additional information about the monocoque body!