Plate/Tag Light

I have a 1953 BL.  The car is still 6 Volt.  I’m trying to find the correct festoon bulb for plate/tag light.  I’ve seen several festoon bulbs advertised on different sites but’s unclear to me which bulb would be the correct one.  Can anyone tell me the correct wattage and more importantly the correct size (length) bulb I should be looking for?  I guess if I can find the LED equivalent that would be work as well.  Appreciate any help with this question.  Thanks.

Kirk