My 1970 Flavia 2000 Coupe has all the holes provided, including outside edge of rear parcel shelf for 3-point [hidden under the vinyl-covered board].
Got my rear belts from KCP Car and Commercial. Can't remember if this link was for the rear belts [standard length] or fronts [extra long]:
https://shop.kcpcarandcommercial.co.uk/epages/100080302.sf/en_GB/?ObjectID=4990521Odd colour but matched my seats and looks good. Very easy to install and balance.