The 70 button in a one year only thing and is twice as long as the other years. If I remember correctly, the 71-74 are interchangeable. Most of the 71s I've seen are chrome, while the 72-74 are black plastic. Ohh in case you are wondering, you cant just take the whole assembly from 71 and bolt it into a 70 frame, reason being is that there is a cage for the button on 71-74 seats. If you want to change them over you will have to weld that cage onto the 70 frame.