Hi Graeme,
not sure what kind of info you are looking for but Sloper magdynos must have changed a bit over the 1927-1935 span of the model. Vintage ones (and perhaps a year or two into the 1930s) used the one-piece alloy-bodied three-brush Lucas magneto. These early ones lacked the clutch between the drive gear on the magneto shaft and the dynamo armature, so they tended to shake themselves to bits. When you see them these days, the bodies are often damaged where the generator armature has tried to escape through the end of the case! Like most Lucas products, the magdynos are stamped with the date code: 930=September 1930 etc.
Leon