Wow! A '64 VW with the original engine. Very impressive.
I recently read through a 1973 general automotive repair guide I have, including recommened oil weights for typical rides of that era. It had separate recommendations for VWs, calling for 30w in most climates, and 20w or 10w (obsolete weights) for progressively colder climates. Perhaps bug enthusiasts might have newer ideas on what an appropriate weight is, but it appears that the "old school" standard for VW's was straight 30w in moderate climates. (The same book recommended 30w, 5w-30, 10w-30, and 10w-40 for Detroit rides, depending on temps.)
Can't say I know much about optimum oils for air cooled engines, but suffice to say, ANY modern API "SL" oil is light years superior to what your typical hippie grandpa might have used in his VW van 35 year ago. A high-mileage oil could be helpful if the seals are compromised; if so, you might hesitate using a synthetic since those oils tend to take advantage of such seal insufficiencies.