Of the 36 GTOs produced from the factory, the first 33 were Series 1s, recognizable by the trio of D shaped ducts that could be covered for aerodynamic slickness or removed for improved radiator cooling. Four of the Series I cars were updated in 1964 with Series II bodies. The 250 GTO was heavily derived from the earlier 250 GT Berlinetta SWB. Ferrari engineers constructed two 250 GTO prototypes in 1961 by converting existing chassis of the SWB. Three 275 GTB/C Speciales were built in 1964/65. Despite their origins, they are sometimes considered developments of the 250 GTO due to similarity of configuration and bodywork.
