One more thing to add to Bob's reply. Your axles do not have the "sleeve" that the factory used on '67-70 axles , SO you will have to use the "regular" 28 splice axle seal and "carefully" slide the axle in through it so the seal surface isn't damaged. 31 spline axles made before '67 ( Galaxie , Thunderbolt , A/FX Mustangs , and '66 427 Fairlanes ) did not have the sleeve . In '67 Ford's "better idea" was to use the sleeve and make a new larger seal ( C7OZ). The sleeves are available now and you could add them and use the large seal if you want.
You ended getting more than you asked for.
Randy