Having a closer look at that engine, it displays a resemblance cosmetically at least with the 175cc OHC Lodola, which in itself was a departure from the trade mark Guzzi single parallel to cylinder cooling fins. The fact this Lodola was in production from 1956-66 nicely spans the date of your excellent find.
I wonder if it shares the OHC design where the cam chain sits within the cylinder and head castings.
