As far as I know the springs were the same from 1975-1993. There were several different weight ratings. The paper tag under the hood showed what springs you had. Most were all 3 leaf. Possibly the HD had 5 leafs. After market may sell a replacement spring that is basically one size fits all so you should replace both of them. All the springs were negative arch. Are you sure yours are bad? They are pretty tough. With the negative arch a lot of people think they are worn out by the look. If they are not riding on the snubber they are most likely ok. You might just need a good shock.