Well since this thread is revived, I might as well add that this chap in UK sells a range of LED bulbs and light boards in 6V and 12V. I fitted one of my 6V motorcycles out with direct replacement LED bulbs in headlamp, side lamp and stop/tail. I have a feeling he even does a dipping headlamp bulb now?
http://www.dynamoregulatorconversion...bulbs-shop.php
Ron