I had a '64 Honda C200 (87cc) that I recently sold. I used Mobil 1 15w50 in it with no problems. Never had a leak and it never used oil. Great little engines!
I had a CL 100 Honda in 1972 and I believe it called for a 30 weight oil...so either a straight 30 or 15-40 such as Rotella would be my suggestion as it still has all the additives needed for an air cooled engine.