Yes, to all of that. If you're using an Altette or pattern of same you'll need to bend the Y shaped bracket that it mounts on to pull it away from the frame / dynamo. The dynamo will have the later 'jelly - mould' cover. I find that I can loosen the engine mount stud that goes through the frame and carries the horn, so it is possible to swivel the horn out of the way whilst tinkering with / fitting the dynamo. Another of BSA's "bits slapped anywhere" solutions. The nacelle versions had the horn in the nacelle of course which, whilst tidy, was inaccessible! The pic is of my Road Rocket. The only difference is that my dynamo has a flat, bakelite cover.