These 4″ wide sills are genuine Rover replacement parts with 6 vents and are for MK3on saloon. Non Genuine is MS63L and a superb copy.
Most/many 1970 cars and Cooper S mk3 had 4 flutes.
They will fit MK1/2 but not original fitment. Closest and best MK1/2 panel compared to this is MS30L with 4 flutes/vents which is a superb panel.