I just converted my 41 to 12V (just saying), but you should be able to source some bright 6V positive earth LED taillight globes. LED globes can be polarity sensitive, so be sure you get ones that will work with positive earth. Ditto with flasher cans.
As others have said, the front park assemblies can be converted to dual filament globe. You can get a conversion kit from C&G. I have installed them for friends in 40's with no problem (the 41 pass car setup is completely different).
Be aware also that some LED globes (especially the high lumen output units) can be larger than stock and may not fit into the modified park/signal space.