in case of no sight glass theer is usally a level plug.
the oil filler looks quite low down on the crank case, it looks about the right hight for it to be doubling up as a level plug. if the oil level is near to the point it would run out of the filler id take that as a big hint that you fill it up to the fill hole.
the old kit is usally very sensibly desinged like that
no level plug......Ref " the oil filler looks quite low down on the crank case, it looks about the right hight for it to be doubling up as a level plug. if the oil level is near to the point it would run out of the filler id take that as a big hint that you fill it up to the fill hole."