Initially, in response to a proposal for a sporty youth-oriented car, a four-seat fastback design study, the Rambler Tarpon, had been built on the compact-sized Rambler American platform. This was shown as a concept car at various auto shows but AMC's current "GEN-1" V8 engine would not fit in the comparatively small Rambler chassis; also the new "GEN-II" V8 designs were still in development, and market research showed that a six-cylinder engine alone would not satisfy potential customers. Management at the small automaker wanted to change "its tune" with "a reasonably sporty 'upsized' response of sorts to Ford's Mustang." The "fastback" appearance was a revival of sedans built after World War II, as demonstrated by the 1940s Nash Ambassador.