Production of the 3500 GT started in late 1957; eighteen cars were built that year, the first handful leaving the factory before Christmas. All 3500 GTs had leather interior and Jaeger instruments. A first Touring convertible prototype was shown at the 1958 Turin Motor Show. But it was a proposal by Carrozzeria Vignale (designed by Michelotti) shown at the 1959 Salon de l'Auto in Paris that went into production as 3500 GT Convertibile. The Convertibile did not feature Touring's Superleggera construction, but rather a steel body with aluminium bonnet, boot lid and optional hard top; it was also built on an 10 cm (3.9 in) shorter wheelbase, and weighed 1,380 kg (3,042 lb). Front disc brakes and limited slip differential became optional in 1959, and were standardized in 1960; rear discs became standard in 1962.