I have a 52 Chevy 3100 that is still 6 volt. I purchased some LED tail lights from Classicparts.com:
(1947-53) LED Taillamp Assembly-Chrome-L-Plastic Red Len
Part # 49-121LR
They assured me these would work with 6 or 12 volts. But on my truck, the only way I could tell they were on was to put my eyeball up to the tail light. Then I discovered you can buy 6-to-12 volt converters. So I installed two of those (one for the brake light wire, and one for the tail light wire). That helped a lot. I got them from Jim Carter:
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ITEM# DESCRIPTION QTY TOTAL
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EL219 Volt Booster Negative Ground Conversion1 $89.50

My dad always told me, "Don't force it, get a bigger hammer".