Well, there's always the Varitronic system for LDs..... not that the engine ever revs high enough to need ignition retarding....
The usual cause of poor lights is that the original flywheel will need remagnetising, and it's only a 6 volt 4-pole system, so getting more than about 28 watts power for lighting is difficult from a single lighting coil. If you could get hold of a flywheel and stator from an LD AVV (12 volt electric start), it's possible to convert to a full 12 Volt DC system, giving around 55 Watts total output, but that also has to power the ignition as well. (Should be enough power to run a 35W halogen headlight, though.) Don't bother with the original electromechanical regulator and plate rectifier - just fit a Wassell combined rectifier/regulator instead.
There was an upgrade system from Scoot RS a few years ago, using a 6 pole SIL electronic flywheel, with a CNC machined fan ring (due to the LD's anticlockwise rotation), and a special flywheel centre to fit to the LD crank. It also used an adaptor plate to fit the GP stator to the LD mag flange. The main fault with that system (IMHO) is that it loaded the much heavier GP flywheel onto the very thin taper of the LD crank - I would expect it would easily shear the crank, given a bit of over-revving or a bad gearchange.