It depends if it regards an overdrive or a non overdrive car.
Non overdrive cars (RHD) have an inner cable with a lenght of 66 inch while overdrive cars (RHD) have an inner cable with a lenght of 72.25 inch or 72 inch. The last difference is depending on what type of speedometer is fitted. Up to chassisnumber A 3812940 AC speedometers were fitted and this instruments have an inner cable with a lenght of 72.25 inch while from chassisnumber A 3812941 Smiths speedometers were fitted and this instruments have an inner cable with a lenght of 72 inch.