If you don't mind spending a little more for rear end safety look at lambertenterprises.com they make 6 volt kits for a lot of cars. The kit in my 40 tail lights from them is the best I have seen.
OldHenery, Try lambertenterprises.com they will make either 6 or 12 volt kits.I went with their 40 conversion kit and now I can be seen at night.Thay are not plug in bulbs they are boards made for your tail lights. hope this helps. Reguards 40f convt