You can't ring an effective 12V from the stock 6V coil. If you are really serious, buy the 12V coil and rectify/regulate to DC and you'll be able to power a decent headlight. Even swapping in an H4 35W bulb @ 12VDC will be a huge upgrade.
I personally don't prefer LED replacement bulbs. Especially given that most are in the 6k heat range, and I love a good 3.5k beam.