Well,that is a Sachs 50 S engine,5 speed and 5,3 HP.Same engine as in my Hercules.The engine came out late 1963,so it is a propper pre65 bike.The 80cc at that period had only 75ccm and was mostly used in the GS Model.that was the ISDT bike.They made a few engines for the US market with 75ccm and autolube system,but that was not a big sucsess.The propper 80cc engine came out in 1981 and had square engine cases and a big alloy barrel like the 125 engine.Hope that will help a bit.
Chrs:Mike