The lever is an adjustment for ambient temperature. N=normal (>59F), C=cold (32-59F), F=freezing (<32F). The Spica pump has a Barometric Pressure Compensator, but no automatic ambient air temperature sensor. The mixture is adjusted richer slightly in the C and F positions. The 69-74 model year pumps had this feature. I believe that the later years did not have it due to EPA regs. They didn't want owners to be able to adjust the mixture at all.
Remember, the emissions regs were the reason that Alfa went to a mechanical fuel injection system at all.