If you do a google search on "Sturmey-Archer" you will find a lot of info on them. In the early days of motorcycles, say about 1910 to 1920, they were quite popular. They would handle the torque of large single and twin cylinder motorcycle.
The business is still running but in Taiwan. Look at their catalog. I have always thought that this would be just the ticket to mount on a single speed moped.