Greetings from Lakewood, Washington. I see that your post Re: Conversion to LED tail light is aging as unanswered. Hopefully you have worked through this project with a great level of success and satisfaction. If so, this post is simply to say hello. If not, I recently converted my 1927 Willys Knight from incandescent bulbs to LED’s, and with exception of the headlights, am really pleased with the results. I am currently restoring a 1923 DB Roadster and (probably) will eventually convert it to LEDS also. The Willys was a necessary conversion because I was super dissatisfied with its 6 volt, positive ground system, and a set of lights that you’d need a flashlight to see if they were even on. This link
https://www.ledlight.com/ will take you to a company which sells LED’s which are a direct exchange for your incandescent bulbs, and will work with your existing sockets. I did change my sockets because I installed turn signals and single bulb/dual filament tail/brake lights and converted the cowl lights to park/turn signals. The only complication you will encounter is the turn signal flasher used with the incandescent bulbs will need to be replaced with one intended for use with the LED’s.
Good luck.
Jack