Just curious how this worked out for you. I've been looking into doing a conversion over to the round LED trailer or truck brake/turn signals but have been preoccupied with other stuff. Do the 4" rounds fit inside nicely or did you have to cut up the housing 'cup' to modify?The next day I completely replaced all of the wires for the rear lighting and now have dependable, super bright full LED tail lights across the rear. I kept the same correct 66 lenses but all 4 light positions are now combined marker/brake and turn signals. I'll deal with a backup light solution in the future. The car has not had backup lights since I got it.
Sure others would like to know too. I cringe when I have to make a left turn into the neighborhood off my busy street knowing that there traffic behind...
Thanks, enjoy and keep up the great work.