Thanks for the courtesy of an acknowledgement. I do occasionally shoot off my, er, fingers without being entirely correct but I did spend some time on this a couple of years ago. (I wouldn't want to be challenging Patrick for the title of CC KnowItAll, as I hold the title so many other places.
)
I did a lot of experimenting a couple of years back trying to brighten up my poor, dim '68 Mustang taillights, since I don't want to get rear-ended once I get it back on the road. I looked at fabbing my own panels (I do have a great deal of electronics fab, prototyping and production experience), and then hit on the idea of using a bracket to hold three fat LED bulbs in the housing. My goal was to come up with something vastly better than original, without heating problems from several high-brightness incandescents, and ideally without permanently modifying major original components like the reflector bowl. The LED bulbs were new then and I acquired several samples while evaluating their qualities.
In general, the bulbs have gotten better in the last few years, with more options in light-radiating style and brightness, still with almost no heat generation.
Sometimes a custom panel is all that will work. I'm still thinking about bringing a kit to market for Mustangs. But LED bulbs have gotten so good and offer fit for almost every need... they're worth checking out before getting into the custom stuff.