[1] A "sporty" youth-oriented convertible was built in 1962 by the Budd Company, an independent body builder in Detroit, Michigan, for evaluation by the fourth largest U.S. automaker at the time, American Motors Corporation (AMC).

[2] The objective of this car was to entice AMC to expand into a new market segment with a low-cost Rambler-based "sports convertible.

[18] The car was styled by Budd with a relatively clean and uncluttered body, giving little indication of its Rambler sedan origin.

A double crease in the beltline suggested a family relationship to the contemporary styling of Rambler's large-sized cars.

[2] Power for the XR-400 was supplied by a standard Ambassador two-barrel 250 hp (186 kW; 253 PS) 327 cu in (5.4 L) AMC V8 engine.

The transmission was an automatic (not typical of sports cars for that time) controlled through a floor console-mounted shift lever.

In classic sports car fashion, the driver had all controls and a complete set of instruments (speedometer, tachometer, as well as gauges for fuel, water temperature, amperes, and oil pressure) that mounted directly ahead of a three-spoke wood-rimmed Nardi (brand) steering wheel.

[3] The press release stated that the concept shows how modifying Rambler Ambassadors results in: Automotive press reports stated that such a new model could have appeared in AMC dealer showrooms, thus establishing a market segment at least six months before Ford's similar Mustang started the "pony car" market.