Z500 or Z400

I'm currently trying to buy an older model road bike to restore to a cafe racer style. At the moment I am looking at a '79 Z400 and a '80 Z500, both in good nick for their ages. Does anyone know much about these bikes, are they reliable, worthwhile bikes for what I am after. I want something thats enjoyable to ride and straight forward to restore. Any feedback would be appreciated. Thanks, Jim