The Miller generators always had a tapered shaft. Not necessary to have a key, the pulley will hold on the taper.
I don't know which type of E3L Velo used, I have modified BSA types to suit. This is just machining the eccentric plate.
I just rewound to 12V an E3L for a Velo. It is the Triumph type with a straight shaft and two keys. The pulley is not the original one obviously.
This type of generator is, I think, more suitable as it has a seal on the drive end. It would be possible to fit a tapered shaft armature into this generator with a bit of modification to the seal sleeve. Hopefully there would be enough clearance for the pulley.