The Zenith 32 NDIX Carburetor was introduced in 1957 for the 1600N and 1600S engines, and continued to be furnished through the 356C in 1965. When rebuilt and set up properly, they provide great service for stock and mildly modified 356 engines.
From Ron LaDow:
For street-driven 356s with engines displacing ~1600 to 1720ccs, it is really hard to beat Zenith carbs.
Their design complements the 616 engine to provide performance where most of us use it: 2,000 – 5,500 rpm. The factory spent many dyno hours and road-test hours making sure that was true and determining the jetting to do so for the various engine specs. And by design or accident, the transition circuitry is superior to any of the alternatives; you do not hear gripes about ‘flat spots’ regarding Zeniths.
Happily, by 1960, Zenith-equipped 356s were fitted with the paper filter elements, so you also get air filtration far superior to any other 356; truly modern tech. But by their design, they are also subject to leakage if not maintained and serviced properly.