Like to chime in here and thank you all for this post and the link as well. I may have never known about this detail if I had not read through this. Over the weekend, we were in a show and the 66 coupe next to us had the 66 style, longer indentations. Our car is a 1-6-66 build, has a date stamp of 10 29 and has the 65, short style indentations. Kind of embarrassing I never noticed this over the years. Nice detail to know and look for.