My proposal is Pazon Altair, which is a simple, reliable and compact system backed by a 7.5 year warranty.
It works well at even low system voltage.
I'd also fit a 12V dual-output coil with a primary resistance of 3 to 4.5 Ohm, as recommended by Pazon.
Please enquire with Pazon about running this set-up in a battery-less environment.
Lucas does not recommend running RM alternators less battery ....
My experience with the Pazon Altair is nothing short of admiration, but, as Knut noted, there's a question on whether or not it will run battery-less. Unable to find any mention of such in their web site. If you get an answer from them, please post to the group.