Actually, the 350GT was the first production car, and offered along side the 400GT from '64-'67 with 120 models. The 400GT started out as an option (400GT Interim) for the 350GT by allowing the buyer to have a larger 4-liter engine; 23 were made from '65-'67. The 400GT 2+2 came around in '66 as the previously mentioned option as a new model. Offered from '66 to '68, 247 were built. The Islero came around to take it's place for 1 year; '68 to '69. The combined Islero 400GT and 400GTS came to 225 models.
During this time, the reason for such low production was thanks to the entry of the '66 Miura P400.
The first Lamborghini car, though, is the 350 GTV, and resides as part of the Isao Noritake collection in Japan. The car itself, has a remarkable history as it was almost completely forgotten about for 22 years.