With the plugs Hubie your Champions are equivalent to a NGK B6HS which is right for your bike. You can go one range colder to a B7HS. With NGK plugs the higher the number the colder the plug.
I run B7HS in all my BSA twins but I live in the country so all my riding is at highway speeds. If I lived in a city or did more rallies at slower speeds etc I would use B6HS, they are less prone to fouling than the B7HS's
You can also use BP6HS or BP7HS which are the same except they have protuding tips. There have been millions of articles written about the pro's and con's of protuding tip plugs so I wont go into that area.
I have a concentric on my plunger Flash, it has the needle in the middle groove and a 240 main jet. I modified mine so it has a changeable pilot jet but thats another story.