Need help with Speedometer cable

The 68 inch I used is #6151659. They also list a 63", but says 2piece 'lower' - and a 40" 'upper' ???. They show that 80" for 1970 and the other ones for 1971 up. I often find that parts listings are either not complete for different years ( or completely wrong) for '75 I frequently have to look up 74 to get any hits.