im not an expert but i dont think so. I have never seen any before for rancheros, although i have a futura front fender that is the same thing as a 66 ranchero and it has 2 small pinstripes allong the crease on the side.
Thanks for checking. I have some factory photos that show the double white or cream lines on a 66 Ranchero, it is from printed literature and just not good enough to get the width and spacing. I can come close to the location even though the photo isn't very large.