I have 12V LED headlights. They don't look weird - you just have to buy normal looking shells. However, you asked for 6V LEDs.
A search for "h4 led bulbs 6v" found this site:
LED BulbsLooks like they should work but I suspect that you are breaking new ground here. They don't seem expensive so worth taking the chance, IMO.
You might find this thread of interest.
LED Headlights