Well, you may or may not have something you can use. The lower A arms are all the same. No, you can't use the J arms on your A arm frame. Now, here's the weird part. J arms were 87-90. The brake calipers, spindles, hubs and rotors are 87-89 early style and 90 and newer late style. Sooooo, IF that J arm setup came off a 1990, you can use the brake, hub, and spindle components on your A arm bike. Here are some pics of the early and late hubs and rotors. The late style is on the left in all pics. You can put all of the early spindle, hub, rotor, and caliper on your A arms, but that would be dumb. You can NOT mix components.