The ISO setting on the camera is only for the camera's meter. If the camera is in manual then the ISO setting on the camera meter has no effect on exposure, period. Only when a camera is in an auto mode does it matter.
In manual you set the ISO with your film choice, 160 here.
The other controls you have to affect exposure are aperture, time, and filters.
Your handheld meter will give you the aperture and time, set them then open up by whatever filter factor is in use.