On my Deuce, I used a AC Cobra tag light. It is very bright because it has two bulbs in it. It is very small and thin ... so there is room for the tag to barely clear the lower body reveal.

FYI ... the AC Cobras used a MG tag light and the tag light is available from most AC Cobra supply places or the MG folks ...

Generally for around 39 dollars or so ...

These folks sell them ...

http://www.cobrarestorers.com/background.htm