Good luck with the DVR frankenstein - I'm sure you'll find it works a treat (assuming the chocolate brushes hold up!) In my experience it's fit and forget with a DVR2, whether in 6 or 12v config. A serious contribution to reliable year-round riding.
Re converting dynamos to run at 12v, there should be no need for special effort these days - a standard-wound field and armature will produce quite enough volts to run and be regulated at 12v, although the cut-in speed goes up obviously. There are fine-wound '12v' field coils available (SRM, Feked etc in the UK) - and fine-wound '12v' armatures too - a combination which promises cut-in and voltage reg at the maker's engine rpm as for a '6v' system. This '12v' combination will offer the usual 60W output, continuous.
A standard E3L dynamo with a 12v regulator should deliver a reasonably safe 85-ish watts max. But there is more heat generated in the field coil at the speeds between when the cut-out cuts in and the regulator starts to regulate. If you keep the original '6v' armature and put in a fine-wound '12v' field coil, the maximum output soars, depending on the wire gauge and number of turns of the field coil winding. In theory, a '6v' wound armature with a '12v' field coil will produce up to 140W output at the same levels of heat dissipation you'd get with a standard 60W output at 6v - but the penalty is high engine rpm before cut-in happens and voltage regulation kicks in.
I currently have my A at 6v with a DVR2 and belt drive and 35W Halogen lamp - very good for what it is. And 2 other twins of other marques, both now with DVR2s. One has a bog-standard-wound armature and field coil, running at 12v with a 45W Halogen lamp, which it has done successfully for over 20 years and a serious mileage. It has in fact run for lengthy periods with a 60/55W halogen up front, which is talking proper illumination. Better with a DVR2 than with a previous (early) JG electronic regulator, and despite the heat dissipation question relating to the field coil, no problems provided one can live with the higher cut-in speed. I can, because I live in the middle of nowhere - but it also worked in London for a long time too. The other is an experiment, running a standard '6v' thick-wound armature with a '12v' fine-wound field winding - but the jury's out as it's very early days and the armature is an unknown quantity. Cut-in speed is very high compared with standard and this may well prove to have been a bad experiment even if the maximum safe output does turn out to be way above the norm for an E3L.
