Found this while hunting for a Galletto workshop manual. Twins and singles:
https://translate.googleusercontent.com/translate_c?depth=1&hl=en&prev=search&rurl=translate.google.co.uk&sl=it&u=http://www.officina-moto-guzzi.it/archiviomoto/Manuali.htm&usg=ALkJrhixhSvKV6DkVNcBO2Copz0FqiA67w