Not quite certain John, and never bollox! I thought that the standard DVR2 didn't have it, whereas the DVR3s & 4s (which ManorMike has moved into other hands now) do.
The quoted requirement is that the field coil resistance for use with a DVR2 should be north of 2.5 ohms, which I assumed meant it'd work OK with the higher resistance '12v' field coils. Although the DR Ltd literature makes no express mention of suitability - it just explains that the max power of the finer-wound parts is very definitely limited to the 60W it says on the tin - I think it's a fair inference that it'll do the job. I'm guessing ManorMike would have explicitly stated if the regulator couldn't be used with the 12v bits, as all the tekkie documentation, and FAQs, are very carefully drafted. But . . . I dunno 100%, can only say I've used them!
The literature goes on to say you can safely get a continuous 80W out of a standard-wound E3L + DVR2. I know I have run my A10, also AMC twins, with continuous loads of 70W+, with heated grips and a 35/35W incandescent bulb, and didn't have any problems. Others have run electronic ignition, even power-hungry Boyer B systems, plus (non-LED) lights, using them. For max power, the standard E3L running with a DVR at 12v is a safe option - IF the higher cut-in speed can be suffered. Which for Owain here, it clearly can't.
RD - I very deliberately didn't say whether that other world of alternators was an inhabitable or uninhabitable one! Different gremlins all of their very own, couldn't agree with you more.
But, as with electronic regulation of our dynamos, modern gizmos that rectify and regulate the output from permanent magnet alternators have made them reliable in my experience. As much as anything because so many possible points of failure in the wiring & switchgear departments can be eliminated.
I have never even thought of using LEDs on my two Lucas alternator bikes (Notruns that do), because the juice is there, like the water pouring over Niagara Falls: there's nothing to stop it! Nor have I thought to invest in an Alton ortenater for any of my dynamo bikes, although a significant number of folk here in France have done so - they have been made pretty reliable now.