Normally the carb 164 has solid discs and the faster 164E has ventilated discs.
They might have standardised vented near the end of production, I'm not sure, but certainly for several years both types of discs were offered, depending on engine power.
Nearly 30 years ago, I converted my first 164, a 1969 model, from solid to vented discs. It was very 'vigorously' driven, and I used to get a lot of noise and brake fade on the solid discs - completely cured when I fitted the 164E brakes.
John
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