Not a problem. From what I've read and some one will correct me if I am wrong but the 85-86 will not interchange with the 87+ rear shocks. But all 87+ will and 85-86 will interchange with each other. thats why if us 85-86 guys want to swap to the newer style swinger we need the entire set up, shock and all.

I am not sure if their are any direct swaps from other bikes. I think I read somewhere that you can swap in a z400 rear with some mild grinding by I'm not 100% on that.