Re: info on 800 serie sterndrive,
1978 - 1985 were the years for the hydro-mechanical and the mechanical Stringers (800 series was the V8, I think). Cobras are a completely different drive (they mount to the transom more like a Merc), and are not compatible with a Stringer at all.
If you've got a Stringer "hole" in the back of your boat, without extensive reconstruction on your transom you can only use a Stringer.
Welcome aboard.