Giorgio Neri and Luciano Bonacini, who were already previously known for their work on the "Nembo" series of Ferraris, had been previously retained by Ferruccio Lamborghini to build the first prototype Lamborghini chassis and engine, the 350 GTV. They had acted as Lamborghini's chassis supplier, before turning that job over to Marchesi once production of the 350 GT was underway. Neri and Bonacini then turned their hand into their interpretation of a high speed Lamborghini GT sports car.
Originally meant to be called the "400 GT Neri and Bonacini" the name was simply shortened to "Monza". The car was reportedly built for an American client for the possibility of racing it in Le Mans. However, homologation problems put a quick end to that plan. The car was eventually sold of at the Barcelona Motor Show to a wealthy Spaniard, where it remained until the owner died in the early 1990s. In 1996, Brooks (now Bonhams) was contacted by the family of the now deceased owner to appraise some other cars, when the 400 GT was discovered in storage. After nine years of negotiations, the car was finally put up for auction at Bonhams for a reported £160,000 to a UK collector.