Looks DOHC to me, so that would be later than 78(here in the US anyway, not sure about the rest of the world). CBX was a 6 cylinder bike, so I'm guessing someone goofed the model name somewhere. The member "Hush" may have some info since he has a retired police bike and I want to say there are a members that are knowledgeable about old police bikes.
Try a search here if you haven't yet. In the list above that says "Single Overhead Cam 4 Forums > General Forums > New Member Introductions", click "Single Overhead Cam 4 Forums" to take you to the uppermost level of the forum, then use the search box that doesn't have Google in it to use the forum's search engine. I haven't used the Google custom search box, so I don't know what kind of results that will give.
